Fix "for" loop initial declarations are only allowed in C99 or C11 mode.

Compiled chromium on loongson3a platform(mips64el architecture) with gcc-4.9.3, occurs errors
about that ‘for’ loop initial declarations are only allowed in C99 or C11 mode.

Bug: 746767

R= dpranke@chromium.org, scottmg@chromium.org

Change-Id: I8809ca16d3e647c967fb7117437a635d8ed05bef
Reviewed-on: https://chromium-review.googlesource.com/578630Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488644}

build/config/compiler/BUILD.gn

@@ -451,19 +451,21 @@ config("compiler") {
     cflags += [ "-fdebug-prefix-map=$absolute_path=." ]
   }
 
-  # C++11 compiler flags setup.
+  # C11/C++11 compiler flags setup.
   # ---------------------------
   if (is_linux || is_android || (is_nacl && is_clang) || current_os == "aix") {
-    # gnu++11 instead of c++11 is needed because some code uses typeof() (a
-    # GNU extension).
+    # gnu11/gnu++11 instead of c11/c++11 is needed because some code uses typeof()
+    # (a GNU extension).
     # TODO(thakis): Eventually switch this to c++11 instead,
     # http://crbug.com/427584
+    cflags_c += [ "-std=gnu11" ]
     cflags_cc += [ "-std=gnu++11" ]
   } else if (!is_win && !is_nacl) {
-    # TODO(mcgrathr) - the NaCl GCC toolchain doesn't support either gnu++11
-    # or c++11; we technically don't need this toolchain any more, but there
+    # TODO(mcgrathr) - the NaCl GCC toolchain doesn't support either gnu11/gnu++11
+    # or c11/c++11; we technically don't need this toolchain any more, but there
     # are still a few buildbots using it, so until those are turned off
     # we need the !is_nacl clause and the (is_nacl && is_clang) clause, above.
+    cflags_c += [ "-std=c11" ]
     cflags_cc += [ "-std=c++11" ]
   }