[PR107130] range-ops: Separate out ffs and popcount optimizations.

[PR107130] range-ops: Separate out ffs and popcount optimizations.

__builtin_popcount and __builtin_ffs were sharing the same range-ops
entry, but the nonzero mask optimization is not valid for ffs.
Separate them out into two entries.

	PR tree-optimization/107130

gcc/ChangeLog:

	* gimple-range-op.cc (class cfn_popcount): Call op_cfn_ffs.
	(class cfn_ffs): New.
	(gimple_range_op_handler::maybe_builtin_call): Separate out
	CASE_CFN_FFS into its own case.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr107130.c: New test.