ios: Disable -Wgnu-folding-constant for .m files.

Bug: 1143700
Change-Id: If1110313fda223d83d17db5600f2041c3e1f6f32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510229
Commit-Queue: Nico Weber <thakis@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822644}

build/config/compiler/BUILD.gn

@@ -1569,6 +1569,11 @@ config("default_warnings") {
           "-Wno-implicit-fallthrough",
         ]
 
+        if (is_ios) {
+          # TODO(https://crbug.com/1143700): Clean up and re-enable.
+          cflags_objc = [ "-Wno-gnu-folding-constant" ]
+        }
+
         if (enable_wmax_tokens) {
           cflags += [ "-Wmax-tokens" ]
         } else {