Fail fast in IR extraction if using local thinLTO and an input (#179)

ThinTLO corpus extraction in extract_ir.py is designed to be used
without an input file (ie an lld params file or a
compile_commands.json). However, if the user passes in an input while
trying to do local thinLTO corpus extraction the extraction might
partially succeed, or even fully succeed without giving any indication
of what might be amiss. This patch makes these configurations error out
to reduce confusion.

Author: boomanaiden154

compiler_opt/tools/extract_ir.py

@@ -320,6 +320,8 @@ def main(argv):
   flags.mark_flags_as_required(['output_dir'])
 
   objs = []
+  if FLAGS.input is not None and FLAGS.thinlto_build == 'local':
+    raise ValueError('--thinlto_build=local cannot be run with --input')
   if FLAGS.input is None:
     if FLAGS.thinlto_build != 'local':
       raise ValueError('--input or --thinlto_build=local must be provided')