update_any_test_checks.py: run from any dir

[nickdesaulniers]

Summary

Allow running llvm/utils/update_any_test_checks.py from working
directories other llvm/utils/.

Fixes:
$ ./llvm/utils/update_any_test_checks.py path/to/foo.ll
utils/update_llc_test_checks.py: not found (used in path/to/foo.ll)

llvm/utils/update_any_test_checks.py

parser.add_argument(
       '--jobs', '-j', default=1, type=int,
       help='Run the given number of jobs in parallel')
   parser.add_argument(
       '--utc-dir', nargs='*',
       help='Additional directories to scan for update_*_test_checks scripts')
   parser.add_argument('tests', nargs='+')
   config = parser.parse_args()
 
-  script_name = os.path.basename(__file__)
   if config.utc_dir:
     utc_search_path = config.utc_dir[:]
   else:
     utc_search_path = []
+  script_name = os.path.abspath(__file__)
   utc_search_path.append(os.path.join(os.path.dirname(script_name),
                                       os.path.pardir))
 
   not_autogenerated = []
   utc_tools = {}
   have_error = False
 
   with ThreadPoolExecutor(max_workers=config.jobs) as executor: