scripts/bloat-o-meter: Support comparing library archives

Library archives (.a) usually contain multiple object files so their
output of nm --size-sort contains lines like:

<omitted for brevity>
00000000000003a8 t run_test

extent-map-tests.o:
<omitted for brevity>

bloat-o-meter currently doesn't handle them which results in errors when
calling .split() on them.  Fix this by simply ignoring them.  This enables
diffing subsystems which generate built-in.a files.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200603103513.3712-1-nborisov@suse.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>