Only add files in GlobSymbolsDir.

I previously skipped directories, but that can still lead to problems.
So instead, only add paths that are files.

Test: Ran over a stack that failed when trying to run llvm-readelf
Test: on a directory. After this fix, everything get line numbers.
Change-Id: Ide39c5a118d78a822057cc3977d0f532595f798b
1 file changed