Unify the name of compiler-rt builtins library on Linux.

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.
Unify the name of compiler-rt builtins library on Linux.

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.