Fix -Wshadow.

This still disables the warning for glmark2 instead of fixing it, to
avoid needing to upstream a patch.

Bug: chromium:794619
Change-Id: Ice602996041d6090c9b09ee81c8ed095c4fa6b2e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3179860
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>

third_party/glmark2/BUILD.gn

@@ -42,6 +42,12 @@ raw_glmark_data_path = rebase_path(glmark_data_path, root_build_dir)
 config("glmark2_common_config") {
   defines = [ "GLMARK_DATA_PATH=\"${raw_glmark_data_path}\"" ]
   include_dirs = [ "src/src" ]
+  cflags = []
+
+  if (is_clang) {
+    cflags += [ "-Wno-shadow" ]
+  }
+
   if (is_win) {
     include_dirs += [ "src/src/include" ]
 
@@ -49,7 +55,7 @@ config("glmark2_common_config") {
     defines += [ "_USE_MATH_DEFINES" ]
 
     if (!is_clang) {
-      cflags = [
+      cflags += [
         # MSVC warns about the copyright character being illegal.
         "/wd4828",