Fix and enable EH for x86-64 Darwin.  Adds
ShortenEHDataFor64Bits as a not-very-accurate
abstraction to cover all the changes in DwarfWriter.
Some cosmetic changes to Darwin assembly code for
gcc testsuite compatibility.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46029 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed