[Supersize] Simple fix to remove LLD-LTO errors.

This CL modifies linker_map_filter.py to add a filter for object
filenames. This enables Supersize to run for LTO (under LLD) without
crashing -- although some data are missing (to be fixed in follow-ups).

Bug: 723798
Change-Id: I90b7439368cca96921d688b0c9db95a599fa2bca
Reviewed-on: https://chromium-review.googlesource.com/982254Reviewed-by: agrieve <agrieve@chromium.org>
Commit-Queue: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546161}

tools/binary_size/libsupersize/linker_map_parser.py

@@ -352,6 +352,8 @@ class MapFileParserLld(object):
             # Treat all literals as stirng literals.
             # FIXME(huangs): Refine this. Checking align == 1 is insufficient.
             sym_maker.cur_sym.full_name = '** lld merge strings'
+          elif cur_obj == 'lto.tmp' or cur_obj.startswith('thinlto-cache'):
+            pass
           else:
             sym_maker.cur_sym.object_path = cur_obj