build: clean up some unnecessary cached variables

The CMAKE_<LANG>_ARCHIVE_FINISH rule doesn't need to be cleared for Darwin
static libraries.  Avoid resetting the variables in the SIP case.  If
CMAKE_RANLIB is cached, then CMake's Ninja generator will invoke ranlib during
installation, not due to the CMAKE_<LANG>_ARCHIVE_FINISH rule.

llvm-svn: 342511