expand: Use the correct mode for store flags for popcount [PR116480]

When expanding popcount used for equal to 1 (or rather __builtin_stdc_has_single_bit),
the wrong mode was bsing used for the mode of the store flags. We were using the mode
of the argument to popcount but since popcount's return value is always int, the mode
of the expansion here should have been the mode of the return type rater than the argument.

Built and tested on aarch64-linux-gnu with no regressions.
Also bootstrapped and tested on x86_64-linux-gnu.

	PR middle-end/116480

gcc/ChangeLog:

	* internal-fn.cc (expand_POPCOUNT): Use the correct mode
	for store flags.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr116480-1.c: New test.
	* gcc.dg/torture/pr116480-2.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>