Revert of 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 3f27efce5fa17c8b3839ecd2bc875cc39e8b944b..40d63af00671a14e62ffa4fbb86bf7e106880d2a 100644
--- a/third_party/mesa/BUILD.gn
+++ b/third_party/mesa/BUILD.gn
@@ -144,15 +144,6 @@
       "/wd4305",  # Truncation from int to float.
       "/wd4334",  # Result of 32-bit shift implicitly converted to 64 bits.
       "/wd4345",  # POD-type default initializers.
-    ]
-  }
-}
-
-config("mesa_libglslcommon_warnings") {
-  if (is_clang) {
-    cflags = [
-      # https://bugs.freedesktop.org/show_bug.cgi?id=91645:
-      "-Wno-overloaded-virtual",
     ]
   }
 }
@@ -260,6 +251,15 @@
     "src/src/glsl/strtod.c",
     "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" ]