Add goma include to mac GM toolchain.

Even though this isn't hooked up on Mac yet, we need the goma include for all toolchains to avoid throwing errors for Goma on Mac users.

TRB=thakis

Review URL: https://codereview.chromium.org/129323002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243644 0039d316-1c4b-4281-b951-d872f2087c98

build/toolchain/mac/BUILD.gn

@@ -9,8 +9,8 @@
 # Should only be running on Mac.
 assert(is_mac || is_ios)
 
-# Clang variables.
-import("../clang.gni")
+import("//build/toolchain/clang.gni")
+import("//build/toolchain/goma.gni")
 
 if (is_clang) {
   cc = rebase_path("//third_party/llvm-build/Release+Asserts/bin/clang", ".", root_build_dir)