Use //build_overrides instead of //build/modules for GN builds.

R=machenbach@chromium.org
BUG=chromium:541791
LOG=N

Review URL: https://codereview.chromium.org/1396743005

Cr-Commit-Position: refs/heads/master@{#31246}

BUILD.gn

@@ -9,7 +9,7 @@ import("//build/config/sanitizers/sanitizers.gni")
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 
 import("snapshot_toolchain.gni")