Reenable unreachable-code warnings.

Change-Id: Ie56967a4b823388f0975384e88be23ff2fceecf7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/504598
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
diff --git a/gn/skia/BUILD.gn b/gn/skia/BUILD.gn
index 7abfd0f..431a481 100644
--- a/gn/skia/BUILD.gn
+++ b/gn/skia/BUILD.gn
@@ -455,7 +455,6 @@
       "-Wno-switch-enum",
       "-Wno-thread-safety-negative",
       "-Wno-undef",
-      "-Wno-unreachable-code",
       "-Wno-unreachable-code-break",
       "-Wno-unreachable-code-return",
       "-Wno-unused-macros",