Use zlib to uncompress debug sections in DWARF parser.

This makes llvm-dwarfdump and llvm-symbolizer understand
debug info sections compressed by ld.gold linker.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180088 91177308-0d34-0410-b5e6-96231b3b80d8