Specify libc++abi location with cmake variable

[lisyarus]

Summary

Trying to build libc++ with libc++abi, I was surprised that, although there exists a cmake variable to specify location of libc++abi includes (LIBCXX_LIBCXXABI_INCLUDE_PATHS), there is no way to provide the location of libc++abi.so.
I suggest adding a variable LIBCXX_LIBCXXABI_LIBRARY for that purpose.

[EricWF]

I currently have a patch out for review that adds support for things like this but for all ABI libraries.
Could you please take a look and see if that meets your use case?

http://reviews.llvm.org/D5038

[lisyarus]

Yes, it looks like your patch fixes this issue.

CMakeLists.txt

   if (LIBCXX_CXX_ABI_INTREE)
     # Link against just-built "cxxabi" target.
     set(CXXABI_LIBNAME cxxabi)
-  else()
+  elseif(LIBCXX_LIBCXXABI_LIBRARY)
+    set(CXXABI_LIBNAME ${LIBCXX_LIBCXXABI_LIBRARY})
+  else()  
     # Assume c++abi is installed in the system, rely on -lc++abi link flag.
     set(CXXABI_LIBNAME "c++abi")
   endif()