Make HIDDEN_DIRECTIVE a function-like macro. NFCI.

This avoids a hack for making it a no-op for windows.

Also explicitly check for _WIN32 instead of assuming it.

Differential Revision: https://reviews.llvm.org/D39156

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@316300 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed