MFC r247960:

  Make ctfconvert work correctly on clang-compiled object files.  Clang
  puts the full original source filename in the STT_FILE entry of the ELF
  symbol table, while gcc saves only the basename.

  Since the DWARF DW_AT_name attribute contains the full source filename,
  both for clang and gcc, ctfconvert takes just the basename of it, for
  matching with the STT_FILE entry.  So when attempting to match with such
  an entry, use its basename, if necessary.

  Reported by:	avg

MFC r247962:

  Fix error in r247960: actually assign the basename to match.iim_file.

  Pointed out by:	avg
  Pointy hat to:	dim