Un-nest configs in GN files.

third_party/mesa/BUILD.gn

Index: third_party/mesa/BUILD.gn
diff --git a/third_party/mesa/BUILD.gn b/third_party/mesa/BUILD.gn
index 40d63af00671a14e62ffa4fbb86bf7e106880d2a..3f27efce5fa17c8b3839ecd2bc875cc39e8b944b 100644
--- a/third_party/mesa/BUILD.gn
+++ b/third_party/mesa/BUILD.gn
@@ -148,6 +148,15 @@ config("mesa_internal_warnings") {
   }
 }
 
+config("mesa_libglslcommon_warnings") {
+  if (is_clang) {
+    cflags = [
+      # https://bugs.freedesktop.org/show_bug.cgi?id=91645:
+      "-Wno-overloaded-virtual",
+    ]
+  }
+}
+
 static_library("mesa_libglslcommon") {
   sources = [
     "$generated_src_dir/mesa/glcpp-lex.c",
@@ -252,15 +261,6 @@ static_library("mesa_libglslcommon") {
     "src/src/glsl/strtod.h",
   ]
 
-  config("mesa_libglslcommon_warnings") {
-    if (is_clang) {
-      cflags = [
-        # https://bugs.freedesktop.org/show_bug.cgi?id=91645:
-        "-Wno-overloaded-virtual",
-      ]
-    }
-  }
-
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   previous_configs = configs