fold: Fix `a * 1j` if a has side effects [PR116454]

fold: Fix `a * 1j` if a has side effects [PR116454]

The problem here was a missing save_expr around arg0 since
it is used twice, once in REALPART_EXPR and once in IMAGPART_EXPR.
Thia adds the save_expr and reformats the code slightly so it is a
little easier to understand.  It excludes the case when arg0 is
a COMPLEX_EXPR since in that case we'll end up with the distinct
real and imaginary parts.  This is important to retain early
optimization in some testcases.

Bootstapped and tested on x86_64-linux-gnu with no regressions.

	PR middle-end/116454

gcc/ChangeLog:

	* fold-const.cc (fold_binary_loc): Fix `a * +-1i`
	by wrapping arg0 with save_expr when it is not COMPLEX_EXPR.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr116454-1.c: New test.
	* gcc.dg/torture/pr116454-2.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
Co-Authored-By: Richard Biener  <rguenther@suse.de>