Bug 1296737 - make clang-cl compile in c++14 mode; r=glandium

MSVC headers have C++14 features without appropriate guards, so clang-cl
needs to be instructed to default to a C++14-compatible mode by default.

build/moz.configure/toolchain.configure

@@ -345,16 +345,20 @@ def check_compiler(compiler, language, target):
     # Note: MSVC, while supporting C++11, still reports 199711L for __cplusplus.
     # Note: this is a strict version check because we used to always add
     # -std=gnu++11.
-    if info.language == 'C++' and info.language_version != 201103:
-        if info.type in ('clang-cl', 'clang', 'gcc'):
+    if info.language == 'C++':
+        if info.type in ('clang', 'gcc') and info.language_version != 201103:
             append_flag('-std=gnu++11')
+        # MSVC 2015 headers include C++14 features, but don't guard them
+        # with appropriate checks.
+        if info.type == 'clang-cl' and info.language_version != 201402:
+            append_flag('-std=c++14')
 
-    # We force clang-cl to emulate Visual C++ 2013 Update 3 with fallback to
+    # We force clang-cl to emulate Visual C++ 2015 Update 2 with fallback to
     # cl.exe.
-    if info.type == 'clang-cl' and info.version != '18.00.30723':
+    if info.type == 'clang-cl' and info.version != '19.00.23918':
         # Those flags are direct clang-cl flags that don't need -Xclang, add
         # them directly.
-        flags.append('-fms-compatibility-version=18.00.30723')
+        flags.append('-fms-compatibility-version=19.00.23918')
         flags.append('-fallback')
 
     # Check compiler target

python/mozbuild/mozbuild/test/configure/test_toolchain_configure.py

@@ -37,6 +37,10 @@ DEFAULT_CXX_11 = {
     '__cplusplus': '201103L',
 }
 
+DEFAULT_CXX_14 = {
+    '__cplusplus': '201402L',
+}
+
 SUPPORTS_GNU99 = {
     '-std=gnu99': DEFAULT_C99,
 }
@@ -45,6 +49,10 @@ SUPPORTS_GNUXX11 = {
     '-std=gnu++11': DEFAULT_CXX_11,
 }
 
+SUPPORTS_CXX14 = {
+    '-std=c++14': DEFAULT_CXX_14,
+}
+
 
 @memoize
 def GCC_BASE(version):
@@ -220,12 +228,12 @@ VS_PLATFORM_X86_64 = {
 # Note: In reality, the -std=gnu* options are only supported when preceded by
 # -Xclang.
 CLANG_CL_3_9 = (CLANG_BASE('3.9.0') + VS('18.00.00000') + DEFAULT_C11 +
-                SUPPORTS_GNU99 + SUPPORTS_GNUXX11) + {
+                SUPPORTS_GNU99 + SUPPORTS_GNUXX11 + SUPPORTS_CXX14) + {
     '*.cpp': {
         '__STDC_VERSION__': False,
         '__cplusplus': '201103L',
     },
-    '-fms-compatibility-version=18.00.30723': VS('18.00.30723')[None],
+    '-fms-compatibility-version=19.00.23918': VS('19.00.23918')[None],
 }
 
 CLANG_CL_PLATFORM_X86 = FakeCompiler(VS_PLATFORM_X86, GCC_PLATFORM_X86[None])
@@ -772,15 +780,16 @@ class WindowsToolchainTest(BaseToolchainTest):
     )
     CLANG_CL_3_9_RESULT = CompilerResult(
         flags=['-Xclang', '-std=gnu99',
-               '-fms-compatibility-version=18.00.30723', '-fallback'],
-        version='18.00.30723',
+               '-fms-compatibility-version=19.00.23918', '-fallback'],
+        version='19.00.23918',
         type='clang-cl',
         compiler='/usr/bin/clang-cl',
         language='C',
     )
     CLANGXX_CL_3_9_RESULT = CompilerResult(
-        flags=['-fms-compatibility-version=18.00.30723', '-fallback'],
-        version='18.00.30723',
+        flags=['-Xclang', '-std=c++14',
+               '-fms-compatibility-version=19.00.23918', '-fallback'],
+        version='19.00.23918',
         type='clang-cl',
         compiler='/usr/bin/clang-cl',
         language='C++',