[libc++abi] Introduce a LIBCXXABI_LIBRARY_VERSION option

That option controls the 'VERSION' attribute of the libc++abi shared
library, which in turn controls the name of the actual dylib being
produced.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@373949 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed