Add internal bitcount functions

Add internal bitcount functions

This patch adds internal function equivalents of all the INT_FN functions.
Unlike the math functions, these functions never set errno and the internal
functions should be exactly equivalent to the built-in ones.  The reason
for defining the internal functions is so that we can extend the
functionality to other modes, in particular vector modes.

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.

gcc/
	* internal-fn.def (DEF_INTERNAL_INT_FN): New macro.
	(CLRSB, CLZ, CTZ, FFS, PARITY, POPCOUNT): New functions.
	* builtins.c (associated_internal_fn): Handle them.

From-SVN: r230475