Add llvm instrinsic function llvm.memset and llvm.memcpy support.

Add llvm instrinsic function llvm.memset and llvm.memcpy support.

SPIR 1.2 require llvm.memcpy support. And llvm will emit llvm.memset sometimes.
So adding a pass to lower these two intrinsic function, and then inline them.

In intrinsic lowering pass, find all llvm.memset and llvm.memcpy and then replace
them with a function call __gen_memset_x and __gen_memcpy_xx, x and xx is for address space.

Because this pass is after clang, but after clang, the unused function seems be stripped, so
implement the __gen_memset_x and __gen_memcpy_xx functions in pre compiled module, then link
them.

Signed-off-by: Yang Rong <rong.r.yang@intel.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>