[libc++abi] Add _LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS
[libc++abi] Add _LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS

It's useful to be able to disable visibility annotations entirely; for
example, if we're building libc++abi static to include in another library,
and we don't want any libc++abi functions getting exported out of that
library. This is a generalization of _LIBCXXABI_DISABLE_DLL_IMPORT_EXPORT.

Differential Revision: https://reviews.llvm.org/D26950

git-svn-id: 6a9f6578bdee8d959f0ed58970538b4ab6004734@288692 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi