Apply -t arg. Switch to std-gnu++14.

build/config/BUILDCONFIG.gn

@@ -130,6 +130,9 @@ declare_args() {
 
   # Compile for Thread Sanitizer to find threading bugs.
   is_tsan = false
+
+  # Use -std=gnu++XX instead of -std=c++XX
+  use_stdgnu = false
 }
 
 # =============================================================================

build/config/compiler/BUILD.gn

@@ -263,10 +263,18 @@ config("compiler") {
 
   # C++14 compiler flags setup.
   # ---------------------------
-  if (is_win) {
-    cc_std = [ "/std:c++14" ]
+  if (use_stdgnu) {
+    if (is_win) {
+      cc_std = [ "/std:gnu++14" ]
+    } else {
+      cc_std = [ "-std=gnu++14" ]
+    }   
   } else {
-    cc_std = [ "-std=c++14" ]
+    if (is_win) {
+      cc_std = [ "/std:c++14" ]
+    } else {
+      cc_std = [ "-std=c++14" ]
+    }
   }
   cflags_cc += cc_std
   cflags_objcc += cc_std

tools/gn.py

@@ -149,6 +149,16 @@ def DontUseClang(args, target_os, host_cpu, target_cpu):
   # We don't have clang on Windows.
   return target_os == 'win'
 
+def SetIsClang(args, gn_args):
+  dont_use_clang = DontUseClang(args, gn_args['target_os'],
+                                      gn_args['host_cpu'],
+                                      gn_args['target_cpu'])
+  gn_args['is_clang'] = args.clang and not dont_use_clang
+  if 'toolchain_prefix' in gn_args:
+     gn_args['is_clang'] = not gn_args['toolchain_prefix']
+  gn_args['is_asan'] = args.asan and gn_args['is_clang']
+  gn_args['is_msan'] = args.msan and gn_args['is_clang']
+  gn_args['is_tsan'] = args.tsan and gn_args['is_clang']
 
 def UseSysroot(args, gn_args):
   # Don't try to use a Linux sysroot if we aren't on Linux.
@@ -157,6 +167,10 @@ def UseSysroot(args, gn_args):
   # Don't use the sysroot if we're given another sysroot.
   if TargetSysroot(args):
     return False
+  # Don't use the sysroot if crossbuild.
+  crossbuild = gn_args['target_cpu'] != gn_args['host_cpu']
+  if crossbuild:
+    return False
   # Otherwise use the sysroot.
   return True
 
@@ -219,16 +233,7 @@ def ToGnArgs(args, mode, arch, target_os):
   if mode == 'product':
     gn_args['dart_runtime_mode'] = 'release'
   else:
-    gn_args['dart_runtime_mode'] = 'develop'
-
-  dont_use_clang = DontUseClang(args, gn_args['target_os'],
-                                      gn_args['host_cpu'],
-                                      gn_args['target_cpu'])
-  gn_args['is_clang'] = args.clang and not dont_use_clang
-
-  gn_args['is_asan'] = args.asan and gn_args['is_clang']
-  gn_args['is_msan'] = args.msan and gn_args['is_clang']
-  gn_args['is_tsan'] = args.tsan and gn_args['is_clang']
+    gn_args['dart_runtime_mode'] = 'develop' 
 
   if not args.platform_sdk and not gn_args['target_cpu'].startswith('arm'):
     gn_args['dart_platform_sdk'] = args.platform_sdk
@@ -245,6 +250,10 @@ def ToGnArgs(args, mode, arch, target_os):
     toolchain = ToolchainPrefix(args)
     if toolchain:
       gn_args['toolchain_prefix'] = ParseStringMap(arch, toolchain)
+
+  SetIsClang(args, gn_args)
+
+  gn_args['use_stdgnu'] = args.use_stdgnu
 
   goma_dir = os.environ.get('GOMA_DIR')
   goma_home_dir = os.path.join(os.getenv('HOME', ''), 'goma')
@@ -414,6 +423,11 @@ def parse_args(args):
   other_group.add_argument('--toolchain-prefix', '-t',
       type=str,
       help='Comma-separated list of arch=/path/to/toolchain-prefix mappings')
+  other_group.add_argument('--use-stdgnu', '-stdgnu',
+      help='Use -std=gnu++XX instead of default -std=c++XX. Needed to crosscompile gproftools.',
+      default=False,
+      dest='use_stdgnu',
+      action='store_true')
   other_group.add_argument('--tsan',
       help='Build with TSAN',
       default=UseTSAN(),