Move constant bitop and bswap folds to fold-const-call.c

Move constant bitop and bswap folds to fold-const-call.c

The only folds left in builtins.c were for constants, so we can remove
the builtins.c handling entirely.

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

gcc/
	* builtins.c (fold_builtin_bitop, fold_builtin_bswap): Delete.
	(fold_builtin_1): Don't call them.
	* fold-const-call.c: Include tm.h.
	(fold_const_call_ss): New variant for integer-to-integer folds.
	(fold_const_call): Call it.

From-SVN: r229921