Only add -isystem for libc++ for C++ files, not C files.

build/config/android/BUILD.gn

Index: build/config/android/BUILD.gn
diff --git a/build/config/android/BUILD.gn b/build/config/android/BUILD.gn
index d4a714b808fe89be6570b4fc6c7cfa300ab5031e..203d917caab3cb871c85c64ee9980c4132142ff3 100644
--- a/build/config/android/BUILD.gn
+++ b/build/config/android/BUILD.gn
@@ -123,13 +123,13 @@ config("compiler") {
 # that is Android-only. Please see that target for advice on what should go in
 # :runtime_library vs. :compiler.
 config("runtime_library") {
-  # NOTE: The libc++ header include paths below are specified in cflags
+  # NOTE: The libc++ header include paths below are specified in cflags_cc
   # rather than include_dirs because they need to come after include_dirs.
   # Think of them like system headers, but don't use '-isystem' because the
   # arm-linux-androideabi-4.4.3 toolchain (circa Gingerbread) will exhibit
   # strange errors. The include ordering here is important; change with
   # caution.
-  cflags = [
+  cflags_cc = [
     "-isystem" +
         rebase_path("$android_libcpp_root/libcxx/include", root_build_dir),
     "-isystem" + rebase_path(