match.pd: Fix up __imag__ .MUL_OVERFLOW simplification [PR123864]

match.pd: Fix up __imag__ .MUL_OVERFLOW simplification [PR123864]

The integer_minus_onep case is really meant for multiplication by
-1, not by (unsigned char)0xff or (unsigned short)0xffff or 0xffffffffU etc.
We've already tested that the first operand is signed (otherwise the
earlier case is used) and also that int_fits_type_p (@1, TREE_TYPE (@0)),
but if @0 is signed and @1 is unsigned all ones with smaller precision
than that, it fits into @0's type, integer_minus_onep will be true
and it still should be handled through the ranges, not as @0 == min.

2026-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/123864
	* match.pd (__builtin_mul_overflow_p (x, cst, (stype) 0) ->
	x > stype_max / cst || x < stype_min / cst): Only check
	integer_minus_onep for signed types.

	* gcc.c-torture/execute/pr123864.c: New test.
	* gcc.dg/torture/pr123864.c: New test.