Suppress MSVC warnings about invalid switch values

Dawn extends texture and buffer usage enums with additional internal
usages.

Bug: dawn:397
Change-Id: Idb3918e1455f596b1e21f109016dd622d8b66732
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/20781
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/common/BUILD.gn

@@ -86,10 +86,11 @@ config("dawn_internal") {
   # Only internal Dawn targets can use this config, this means only targets in
   # this BUILD.gn file.
   visibility = [ ":*" ]
+  cflags = []
 
   # Enable more warnings that were found when using Dawn in other projects
   if (is_clang) {
-    cflags = [
+    cflags += [
       "-Wconditional-uninitialized",
       "-Wcstring-format-directive",
       "-Wc++11-narrowing",
@@ -123,6 +124,12 @@ config("dawn_internal") {
       "-Wno-microsoft-enum-value",
     ]
   }
+
+  if (!is_clang && is_win) {
+    # Dawn extends wgpu enums with internal enums.
+    # MSVC considers these invalid switch values. crbug.com/dawn/397.
+    cflags += [ "/wd4063" ]
+  }
 }
 
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