[ThinLTO] Hash more part of the config to build cache entries

This has been fixed in the "new" LTO API used by Gold/LLD, this is
fixing the same issue in the libLTO API used by ld64 (amongst other)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291518 91177308-0d34-0410-b5e6-96231b3b80d8