[libcxx] Make libc++.so a linker script by default on most platforms.
This patch turns on LIBCXX_ENABLE_ABI_LINKER_SCRIPT by default whenever LLVM_HAVE_LINK_VERSION_SCRIPT is ON. This turns out to be whenever:
- WIN32 is not defined.
2 UNIX is defined.
- APPLE is not defined.
While LLVM_HAVE_LINK_VERSION_SCRIPT is meant to reflect exactly what we are asking I think it's close enough.
After committing this patch Linux users will no longer have to use "-lc++abi" explicitly!
Reviewers: mclow.lists, danalbert, compnerd, jroelofs
Subscribers: emaste, rengolin, cbergstrom, cfe-commits
Differential Revision: http://reviews.llvm.org/D13739