[ELF] - Make LLD remove gnu-lib compression prefix (".z") after decompression when using -r

This is PR33289.

Previously LLD leaved section naming as is and that lead to wrong result,
because we decompress sections when using -r,
and hence should remove ".z" prefix.

Differential revision: https://reviews.llvm.org/D33885

llvm-svn: 304711