Disable thumb when building tcmalloc

This fixes the arm/linux build which is currently
broken because third_party/tc_malloc is not currently
buildable with -mthumb:

atomicops-internals-arm-v6plus.h:268:8:
 error: instruction requires: arm-mode "strexd  %0, %2, [%3]\n"`

BUG=564059

Review-Url: https://codereview.chromium.org/2515503002
Cr-Original-Commit-Position: refs/heads/master@{#433052}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 446886fca650e9239999df634ef6bc890b95680d

config/BUILDCONFIG.gn

@@ -471,6 +471,7 @@ default_compiler_configs = [
   "//build/config/compiler:compiler",
   "//build/config/compiler:clang_stackrealign",
   "//build/config/compiler:compiler_arm_fpu",
+  "//build/config/compiler:compiler_arm_thumb",
   "//build/config/compiler:chromium_code",
   "//build/config/compiler:default_include_dirs",
   "//build/config/compiler:default_optimization",

config/compiler/BUILD.gn

@@ -534,13 +534,6 @@ config("compiler_cpu_abi") {
           "-march=$arm_arch",
           "-mfloat-abi=$arm_float_abi",
         ]
-        if (arm_use_thumb) {
-          cflags += [ "-mthumb" ]
-          if (is_android && !is_clang) {
-            # Clang doesn't support this option.
-            cflags += [ "-mthumb-interwork" ]
-          }
-        }
       }
       if (arm_tune != "") {
         cflags += [ "-mtune=$arm_tune" ]
@@ -765,6 +758,17 @@ config("compiler_arm_fpu") {
   }
 }
 
+config("compiler_arm_thumb") {
+  if (current_cpu == "arm" && arm_use_thumb && is_posix &&
+      !(is_mac || is_ios || is_nacl)) {
+    cflags = [ "-mthumb" ]
+    if (is_android && !is_clang) {
+      # Clang doesn't support this option.
+      cflags += [ "-mthumb-interwork" ]
+    }
+  }
+}
+
 # runtime_library -------------------------------------------------------------
 #
 # Sets the runtime library and associated options.