Fix building on macOS after SVN r314492

That commit incorrectly expanded the assumption that defined(__APPLE__)
implies SjLj exception handling, which only is true within ARM
code sections.

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@314695 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed