[mach-o] add parsing of x86 relocations

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@212239 91177308-0d34-0410-b5e6-96231b3b80d8
[mach-o] Fix warning on enumeration cases not handled

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@212241 91177308-0d34-0410-b5e6-96231b3b80d8