Add ifdefs around ELF specific parts of UnwindRegisters*.S for arm

This allows using dwarf exceptions on MinGW/ARM.

Differential Revision: https://reviews.llvm.org/D39534

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@317423 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed