diff --git a/browser/installer/Makefile.in b/browser/installer/Makefile.in
index 2453b22589ad..2e55ed4b83dc 100644
--- a/browser/installer/Makefile.in
+++ b/browser/installer/Makefile.in
@@ -129,13 +129,6 @@ endif
 endif
 DEFINES += -DLPROJ_ROOT=$(LPROJ_ROOT)
 
-ifdef CLANG_CXX
-DEFINES += -DCLANG_CXX
-endif
-ifdef CLANG_CL
-DEFINES += -DCLANG_CL
-endif
-
 ifdef LLVM_SYMBOLIZER
 DEFINES += -DLLVM_SYMBOLIZER=$(notdir $(LLVM_SYMBOLIZER))
 endif
diff --git a/config/config.mk b/config/config.mk
index 79ad49560cb2..b270dd9849a1 100644
--- a/config/config.mk
+++ b/config/config.mk
@@ -262,7 +262,7 @@ export LIB
 endif
 
 ifdef MOZ_USING_CCACHE
-ifdef CLANG_CXX
+ifeq ($(CC_TYPE),clang)
 export CCACHE_CPP2=1
 endif
 endif
diff --git a/config/rules.mk b/config/rules.mk
index 5a10dbbb89f9..7449af7a1bb1 100644
--- a/config/rules.mk
+++ b/config/rules.mk
@@ -128,7 +128,7 @@ LINK_PDBFILE = $(basename $@).pdb
 endif
 endif
 
-ifndef GNU_CC
+ifeq ($(CC_TYPE),clang-cl)
 
 ifdef SIMPLE_PROGRAMS
 COMPILE_PDB_FLAG ?= -Fd$(basename $(@F)).pdb
@@ -140,7 +140,7 @@ ifdef MOZ_DEBUG
 CODFILE=$(basename $(@F)).cod
 endif
 
-endif # !GNU_CC
+endif # CC_TYPE == clang-cl
 endif # WINNT
 
 ifeq (arm-Darwin,$(TARGET_CPU)-$(OS_TARGET))
@@ -295,7 +295,7 @@ endif
 # MINGW32
 #
 ifeq ($(OS_ARCH),WINNT)
-ifdef GNU_CC
+ifneq ($(CC_TYPE),clang-cl)
 DSO_LDOPTS += -Wl,--out-implib -Wl,$(IMPORT_LIBRARY)
 endif
 endif
@@ -308,11 +308,11 @@ IFLAGS1 = -m 644
 IFLAGS2 = -m 755
 endif
 
-ifeq (_WINNT,$(GNU_CC)_$(OS_ARCH))
+ifeq (clang-cl_WINNT,$(CC_TYPE)_$(OS_ARCH))
 OUTOPTION = -Fo# eol
 else
 OUTOPTION = -o # eol
-endif # WINNT && !GNU_CC
+endif # WINNT && clang-cl
 
 ifeq (,$(CROSS_COMPILE))
 HOST_OUTOPTION = $(OUTOPTION)
@@ -419,12 +419,12 @@ endef
 $(PROGRAM): $(PROGOBJS) $(STATIC_LIBS) $(EXTRA_DEPS) $(call resfile,$(PROGRAM)) $(GLOBAL_DEPS) $(call mkdir_deps,$(FINAL_TARGET))
 	$(REPORT_BUILD)
 	$(call BUILDSTATUS,START_Program $(@F))
-ifeq (_WINNT,$(GNU_CC)_$(OS_ARCH))
+ifeq (clang-cl_WINNT,$(CC_TYPE)_$(OS_ARCH))
 	$(LINKER) -OUT:$@ -PDB:$(LINK_PDBFILE) -IMPLIB:$(basename $(@F)).lib $(WIN32_EXE_LDFLAGS) $(LDFLAGS) $(MOZ_PROGRAM_LDFLAGS) $($(notdir $@)_OBJS) $(filter %.res,$^) $(STATIC_LIBS) $(SHARED_LIBS) $(OS_LIBS)
-else # !WINNT || GNU_CC
+else # !WINNT || !clang-cl
 	$(call EXPAND_CC_OR_CXX,$@) -o $@ $(COMPUTED_CXX_LDFLAGS) $($(notdir $@)_OBJS) $(filter %.res,$^) $(WIN32_EXE_LDFLAGS) $(LDFLAGS) $(STATIC_LIBS) $(MOZ_PROGRAM_LDFLAGS) $(SHARED_LIBS) $(OS_LIBS)
 	$(call py_action,check_binary $(@F),$@)
-endif # WINNT && !GNU_CC
+endif # WINNT && clang-cl
 
 ifdef ENABLE_STRIP
 	$(STRIP) $(STRIP_FLAGS) $@
@@ -437,7 +437,7 @@ endif
 $(HOST_PROGRAM): $(HOST_PROGOBJS) $(HOST_LIBS) $(HOST_EXTRA_DEPS) $(GLOBAL_DEPS) $(call mkdir_deps,$(DEPTH)/dist/host/bin)
 	$(REPORT_BUILD)
 	$(call BUILDSTATUS,START_Program $(@F))
-ifeq (_WINNT,$(GNU_CC)_$(HOST_OS_ARCH))
+ifeq (clang-cl_WINNT,$(HOST_CC_TYPE)_$(HOST_OS_ARCH))
 	$(HOST_LINKER) -OUT:$@ -PDB:$(HOST_PDBFILE) $($(notdir $@)_OBJS) $(WIN32_EXE_LDFLAGS) $(HOST_LDFLAGS) $(HOST_LINKER_LIBPATHS) $(HOST_LIBS) $(HOST_EXTRA_LIBS)
 else
 ifeq ($(HOST_CPP_PROG_LINK),1)
@@ -464,12 +464,12 @@ $(foreach p,$(SIMPLE_PROGRAMS),$(eval $(call simple_program_deps,$(p))))
 $(SIMPLE_PROGRAMS):
 	$(REPORT_BUILD)
 	$(call BUILDSTATUS,START_Program $(@F))
-ifeq (_WINNT,$(GNU_CC)_$(OS_ARCH))
+ifeq (clang-cl_WINNT,$(CC_TYPE)_$(OS_ARCH))
 	$(LINKER) -out:$@ -pdb:$(LINK_PDBFILE) $($@_OBJS) $(filter %.res,$^) $(WIN32_EXE_LDFLAGS) $(LDFLAGS) $(MOZ_PROGRAM_LDFLAGS) $(STATIC_LIBS) $(SHARED_LIBS) $(OS_LIBS)
 else
 	$(call EXPAND_CC_OR_CXX,$@) $(COMPUTED_CXX_LDFLAGS) -o $@ $($@_OBJS) $(filter %.res,$^) $(WIN32_EXE_LDFLAGS) $(LDFLAGS) $(STATIC_LIBS) $(MOZ_PROGRAM_LDFLAGS) $(SHARED_LIBS) $(OS_LIBS)
 	$(call py_action,check_binary $(@F),$@)
-endif # WINNT && !GNU_CC
+endif # WINNT && clang-cl
 
 ifdef ENABLE_STRIP
 	$(STRIP) $(STRIP_FLAGS) $@
@@ -482,7 +482,7 @@ endif
 $(HOST_SIMPLE_PROGRAMS): host_%$(HOST_BIN_SUFFIX): $(HOST_LIBS) $(HOST_EXTRA_DEPS) $(GLOBAL_DEPS)
 	$(REPORT_BUILD)
 	$(call BUILDSTATUS,START_Program $(@F))
-ifeq (WINNT_,$(HOST_OS_ARCH)_$(GNU_CC))
+ifeq (WINNT_clang-cl,$(HOST_OS_ARCH)_$(HOST_CC_TYPE))
 	$(HOST_LINKER) -OUT:$@ -PDB:$(HOST_PDBFILE) $($(notdir $@)_OBJS) $(WIN32_EXE_LDFLAGS) $(HOST_LDFLAGS) $(HOST_LINKER_LIBPATHS) $(HOST_LIBS) $(HOST_EXTRA_LIBS)
 else
 ifneq (,$(HOST_CPPSRCS)$(USE_HOST_CXX))
@@ -538,10 +538,10 @@ $(SHARED_LIBRARY): $(OBJS) $(call resfile,$(SHARED_LIBRARY)) $(STATIC_LIBS) $(EX
 	$(REPORT_BUILD)
 	$(call BUILDSTATUS,START_SharedLib $@)
 	$(RM) $@
-	$(MKSHLIB) $(if $(filter _WINNT,$(GNU_CC)_$(OS_ARCH)),-IMPLIB:$(basename $(@F)).lib )$($(notdir $@)_OBJS) $(filter %.res,$^) $(RELRHACK_LDFLAGS) $(LDFLAGS) $(STATIC_LIBS) $(SHARED_LIBS) $(EXTRA_DSO_LDOPTS) $(MOZ_GLUE_LDFLAGS) $(OS_LIBS)
+	$(MKSHLIB) $(if $(filter clang-cl_WINNT,$(CC_TYPE)_$(OS_ARCH)),-IMPLIB:$(basename $(@F)).lib )$($(notdir $@)_OBJS) $(filter %.res,$^) $(RELRHACK_LDFLAGS) $(LDFLAGS) $(STATIC_LIBS) $(SHARED_LIBS) $(EXTRA_DSO_LDOPTS) $(MOZ_GLUE_LDFLAGS) $(OS_LIBS)
 	$(call py_action,check_binary,$@)
 
-ifeq (_WINNT,$(GNU_CC)_$(OS_ARCH))
+ifeq (clang-cl_WINNT,$(CC_TYPE)_$(OS_ARCH))
 endif	# WINNT && !GCC
 	chmod +x $@
 ifdef ENABLE_STRIP
diff --git a/js/src/Makefile.in b/js/src/Makefile.in
index 22c4251098b9..9202f5efb256 100644
--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -79,10 +79,10 @@ CFLAGS += $(MOZ_ZLIB_CFLAGS)
 ifeq ($(OS_ARCH),SunOS)
 ifeq ($(TARGET_CPU),sparc)
 
-ifdef GNU_CC
+ifneq ($(CC_TYPE),clang-cl)
 CFLAGS   += -mcpu=v9
 CXXFLAGS += -mcpu=v9
-endif # GNU_CC
+endif # !clang-cl
 
 endif
 endif
diff --git a/python/mozbuild/mozbuild/action/test_archive.py b/python/mozbuild/mozbuild/action/test_archive.py
index f5dd893d3bbf..d64febcc1fbc 100644
--- a/python/mozbuild/mozbuild/action/test_archive.py
+++ b/python/mozbuild/mozbuild/action/test_archive.py
@@ -688,7 +688,10 @@ if buildconfig.substs.get("MOZ_CODE_COVERAGE"):
     )
 
 
-if buildconfig.substs.get("MOZ_ASAN") and buildconfig.substs.get("CLANG_CL"):
+if (
+    buildconfig.substs.get("MOZ_ASAN")
+    and buildconfig.substs.get("CC_TYPE") == "clang-cl"
+):
     asan_dll = {
         "source": buildconfig.topobjdir,
         "base": "dist/bin",
diff --git a/python/mozbuild/mozbuild/frontend/context.py b/python/mozbuild/mozbuild/frontend/context.py
index d09bbdbe3c0b..621404d55461 100644
--- a/python/mozbuild/mozbuild/frontend/context.py
+++ b/python/mozbuild/mozbuild/frontend/context.py
@@ -484,7 +484,7 @@ class LinkFlags(BaseCompileFlags):
         if all(
             [
                 self._context.config.substs.get("OS_ARCH") == "WINNT",
-                not self._context.config.substs.get("GNU_CC"),
+                self._context.config.substs.get("CC_TYPE") == "clang-cl",
                 not self._context.config.substs.get("MOZ_DEBUG"),
             ]
         ):
diff --git a/python/mozbuild/mozbuild/frontend/data.py b/python/mozbuild/mozbuild/frontend/data.py
index b958680aa5da..b2b11736ae3b 100644
--- a/python/mozbuild/mozbuild/frontend/data.py
+++ b/python/mozbuild/mozbuild/frontend/data.py
@@ -870,10 +870,10 @@ class SharedLibrary(Library):
                     + self.symbols_file
                 )
             elif os_target == "WINNT":
-                if context.config.substs.get("GNU_CC"):
-                    self.symbols_link_arg = self.symbols_file
-                else:
+                if context.config.substs.get("CC_TYPE") == "clang-cl":
                     self.symbols_link_arg = "-DEF:" + self.symbols_file
+                else:
+                    self.symbols_link_arg = self.symbols_file
             elif context.config.substs.get("GCC_USE_GNU_LD"):
                 self.symbols_link_arg = "-Wl,--version-script," + self.symbols_file
 
diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
index 635d69514987..c77fef7a9742 100644
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -1297,10 +1297,10 @@ class TreeMetadataEmitter(LoggingMixin):
             else:
                 path = deffile.target_basename
 
-            if context.config.substs.get("GNU_CC"):
-                computed_link_flags.resolve_flags("DEFFILE", [path])
-            else:
+            if context.config.substs.get("CC_TYPE") == "clang-cl":
                 computed_link_flags.resolve_flags("DEFFILE", ["-DEF:" + path])
+            else:
+                computed_link_flags.resolve_flags("DEFFILE", [path])
 
         dist_install = context["DIST_INSTALL"]
         if dist_install is True:
@@ -1312,9 +1312,10 @@ class TreeMetadataEmitter(LoggingMixin):
         # the moment because USE_STATIC_LIBS can be set after a template
         # returns. Eventually, with context-based templates, it will be
         # possible.
-        if context.config.substs.get(
-            "OS_ARCH"
-        ) == "WINNT" and not context.config.substs.get("GNU_CC"):
+        if (
+            context.config.substs.get("OS_ARCH") == "WINNT"
+            and context.config.substs.get("CC_TYPE") == "clang-cl"
+        ):
             use_static_lib = context.get(
                 "USE_STATIC_LIBS"
             ) and not context.config.substs.get("MOZ_ASAN")
diff --git a/python/mozbuild/mozbuild/test/frontend/test_emitter.py b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
index ee5d5e14673a..b37362d9311e 100644
--- a/python/mozbuild/mozbuild/test/frontend/test_emitter.py
+++ b/python/mozbuild/mozbuild/test/frontend/test_emitter.py
@@ -277,7 +277,7 @@ class TestEmitterBasic(unittest.TestCase):
             "link-flags",
             extra_substs={
                 "OS_ARCH": "WINNT",
-                "GNU_CC": "",
+                "CC_TYPE": "clang-cl",
                 "MOZ_OPTIMIZE": "1",
                 "MOZ_DEBUG_LDFLAGS": ["-DEBUG"],
                 "MOZ_DEBUG_SYMBOLS": "1",
@@ -295,7 +295,7 @@ class TestEmitterBasic(unittest.TestCase):
             "link-flags",
             extra_substs={
                 "OS_ARCH": "WINNT",
-                "GNU_CC": "",
+                "CC_TYPE": "clang-cl",
                 "MOZ_DMD": "1",
                 "MOZ_DEBUG_LDFLAGS": ["-DEBUG"],
                 "MOZ_DEBUG_SYMBOLS": "1",
@@ -366,7 +366,12 @@ class TestEmitterBasic(unittest.TestCase):
 
     def test_host_rtl_flag(self):
         reader = self.reader(
-            "host-compile-flags", extra_substs={"OS_ARCH": "WINNT", "MOZ_DEBUG": "1"}
+            "host-compile-flags",
+            extra_substs={
+                "OS_ARCH": "WINNT",
+                "MOZ_DEBUG": "1",
+                "CC_TYPE": "clang-cl",
+            },
         )
         sources, ldflags, flags, lib, target_flags = self.read_topsrcdir(reader)
         self.assertIsInstance(flags, ComputedFlags)
diff --git a/toolkit/system/windowsDHCPClient/tests/gtest/moz.build b/toolkit/system/windowsDHCPClient/tests/gtest/moz.build
index b87007a35375..dffc218bed38 100644
--- a/toolkit/system/windowsDHCPClient/tests/gtest/moz.build
+++ b/toolkit/system/windowsDHCPClient/tests/gtest/moz.build
@@ -17,5 +17,5 @@ LOCAL_INCLUDES += [
 
 FINAL_LIBRARY = "xul-gtest"
 
-if CONFIG["GNU_CXX"]:
+if CONFIG["CC_TYPE"] != "clang-cl":
     CXXFLAGS += ["-Wshadow"]