Call ProcessCompileDatabaseIfNeeded in generate_compdb.py.

As mentioned in https://crrev.com/c/1114413.

Bug: 396230
Change-Id: I2bd1d0b6123bf01f78ea0f88ebf45fc85cbe0f38
Reviewed-on: https://chromium-review.googlesource.com/1124067Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Owen Rodley <orodley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572406}

tools/clang/scripts/generate_compdb.py

@@ -30,7 +30,9 @@ def main(argv):
       help='Path to build directory')
   args = parser.parse_args()
 
-  print json.dumps(compile_db.GenerateWithNinja(args.p))
+  print json.dumps(
+      compile_db.ProcessCompileDatabaseIfNeeded(
+          compile_db.GenerateWithNinja(args.p)))
 
 
 if __name__ == '__main__':