[CMake] Split linked libraries for shared and static libc++

Some linker libraries are only needed for shared libc++, some only
for static libc++, combining these together in LIBCXX_LIBRARIES and
LIBCXX_INTERFACE_LIBRARIES can introduce unnecessary dependencies.

This changes splits those up into LIBCXX_SHARED_LIBRARIES and
LIBCXX_STATIC_LIBRARIES matching what libc++abi already does.

Differential Revision: https://reviews.llvm.org/D57872

llvm-svn: 358614