Changes exception for gyp files to only gyp files in build/

I changed analyzer such that if a gyp file (or an included gypi file)
changes all targets in the gyp file are marked as changed. This means
I should no longer have to special case gyp files. I'm leaving the
exception in place for any gyp files in build as any change to those
really needs to recompile the world.

BUG=109173
TEST=none
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/512693004

Cr-Commit-Position: refs/heads/master@{#292392}

testing/buildbot/trybot_analyze_config.json

 {
   "exclusions": [
-    ".*gyp[i]?",
+    "build/.*gyp[i]?",
     "build/android/pylib",
     "build/compiler_version.py",
     "build/get_landmines.py",