[bazel] Add location for G3 define

Change-Id: I7811e0e70e4959be8caa1cab9e4f1fa3421d72d1
Bug: skia:13211
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/536596
Reviewed-by: Jorge Betancourt <jmbetancourt@google.com>

bazel/BUILD.bazel

@@ -3,6 +3,9 @@ load("//bazel:macros.bzl", "cc_library", "select_multi")
 licenses(["notice"])
 
 GENERAL_DEFINES = [
+    # The following comment is load-bearing. It will be replace via regex when we build for Google3
+    # Do not remove it or we won't be able to properly define SK_BUILD_FOR_GOOGLE3
+    # REPLACE_WHEN_BUILDING_IN_GOOGLE3
     "SK_HAS_ANDROID_CODEC",
     "SKIA_IMPLEMENTATION=1",
 ] + select({