Add a new LIBUNWIND_WEAK_PTHREAD Cmake option to force
calls into the pthread library use weak symbols.

This option allows libpthread to be a weak dependency rather
than a hard one.

Differential Revision: https://reviews.llvm.org/D60285

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@360610 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed