Allow libc++ to be built with CMake from within the LLVM tree. The libc++ part is just some renaming as the variable  was already in use, conflicting with something else in the LLVM tree.  Contributed by Ruben Van Boxem.
Allow libc++ to be built with CMake from within the LLVM tree. The libc++ part is just some renaming as the variable  was already in use, conflicting with something else in the LLVM tree.  Contributed by Ruben Van Boxem.

git-svn-id: 273b07cebdae5845b4a75aae04570b978db9eb50@153036 91177308-0d34-0410-b5e6-96231b3b80d8

lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx