XCore target: add GCCBuiltin to four intrinsics

The following are made available by clang in the XCore ABI
	__builtin_bitrev
	__builtin_getid
	__builtin_getps
	__builtin_setps

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187566 91177308-0d34-0410-b5e6-96231b3b80d8