[clang] Create install targets for non-shared libraries

I don't see a reason for these to not have install targets created,
which in turn allows them to be bundled in distributions. This doesn't
affect the "install" target, since that just runs all CMake install
rules (and we were already creating install rules for these).

Differential Revision: https://reviews.llvm.org/D58268

llvm-svn: 354140