Skip building unused parts when targeting SJLJ

When SJLJ exceptions are used, those functions aren't used.

This fixes build failures on ARM with SJLJ enabled (e.g. on armv7/iOS)
when built using the CMake project files.

Differential Revision: https://reviews.llvm.org/D38249

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@314197 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed