Revert "Disable -Wmemset-transposed-args when building with ToT clang"

This reverts commit 24c0d3d2.

Reason for revert: Try the warning again after Clang r337706.

Original change's description:
> Disable -Wmemset-transposed-args when building with ToT clang
> 
> This warning has a few false positives in ffmpeg.
> 
> TBR=thakis@chromium.org
> BUG=866202
> 
> Change-Id: I08634bdeabe6e30225d37941b078c540c21a74bc
> Reviewed-on: https://chromium-review.googlesource.com/1145887
> Reviewed-by: Reid Kleckner <rnk@chromium.org>
> Commit-Queue: Reid Kleckner <rnk@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#577055}

TBR=thakis@chromium.org,rnk@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 866202
Change-Id: I2d2dceca60f19b20554f96dea0c7d8bb2dc6792d
Reviewed-on: https://chromium-review.googlesource.com/1155497Reviewed-by: Reid Kleckner <rnk@chromium.org>
Commit-Queue: Reid Kleckner <rnk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579213}

build/config/compiler/BUILD.gn

@@ -1470,9 +1470,6 @@ config("default_warnings") {
           # TODO(thakis): Only for no_chromium_code? http://crbug.com/505314
           "-Wno-ignored-pragma-optimize",
         ]
-        if (llvm_force_head_revision) {
-          cflags += [ "-Wno-memset-transposed-args" ]
-        }
       }
     }
   }