Add build/mac_toolchain to trybot_analyze_config.

BUG=

Review-Url: https://codereview.chromium.org/2346323002
Cr-Commit-Position: refs/heads/master@{#419558}

testing/buildbot/trybot_analyze_config.json

@@ -16,6 +16,7 @@
       "build/get_landmines.py",
       "build/gyp_chromium",
       "build/linux/sysroot_ld_path.sh",
+      "build/mac_toolchain.py",
       "build/toolchain/get_concurrent_links.py",
       "build/toolchain/mac/.*py",
       "build/util/lib/common/unittest_util.py",