gn/clang: Only pass -Wno-reserved-user-defined-literal on Linux and Android.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 7a00b9384cf9ad756b5e3bcb9a55cfdfbb6b5898..b305d86b9c89cee7aad147e65b8ffc314b29203a 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -959,11 +959,15 @@ if (is_clang) {
     # which we no longer use. Check if it makes sense to remove
     # this as well. http://crbug.com/316352
     "-Wno-unneeded-internal-declaration",
-
-    # TODO(thakis): Remove, http://crbug.com/263960
-    "-Wno-reserved-user-defined-literal",
   ]
 
+  if (is_posix && !is_mac && !is_ios) {
+    default_warning_flags += [
+      # TODO(thakis): Remove, http://crbug.com/263960
+      "-Wno-reserved-user-defined-literal",
+    ]
+  }
+
   # NaCl's Clang compiler and Chrome's hermetic Clang compiler will almost
   # always have different versions. Certain flags may not be recognized by
   # one version or the other.