[libunwind] Clean up macro usage.

Convention in libunwind is to use !defined(FOOT) not !FOO.

Differential Revision: https://reviews.llvm.org/D31078



git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@299225 91177308-0d34-0410-b5e6-96231b3b80d8
14 files changed