Call it "libclang_rt.builtins-<arch>.a" to be consistent
with sanitizers/profile libraries naming. Modify Makefile
and CMake build systems and Clang driver accordingly.

Fixes PR19822.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209474 91177308-0d34-0410-b5e6-96231b3b80d8