This matches the corresponding change to libcxx headers in
dfa88927ae.
This avoids needing to define _LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS
when building libcxxabi tests, for two reasons:
- It defaults to normal linkage (as opposed to dllimport), fixing
linking of a static library version of libcxx/libcxxabi
- It avoids issues with using dllimport declarations on symbols when
including cxxabi implementations into the testcase itself
Differential Revision: https://reviews.llvm.org/D148441
692518d04b