asan: Fix ICE during instrumentation of returns_twice calls [PR112709]

The following patch on top of the previously posted ubsan/gimple-iterator
one handles asan the same.  While the case of returning by hidden reference
is handled differently because of the first recently posted asan patch,
this deals with instrumentation of the aggregates returned in registers
case as well as instrumentation of loads from aggregate memory in the
function arguments of returns_twice calls.

2024-03-13  Jakub Jelinek  <jakub@redhat.com>

	PR sanitizer/112709
	* asan.cc (maybe_create_ssa_name, maybe_cast_to_ptrmode,
	build_check_stmt, maybe_instrument_call, asan_expand_mark_ifn): Use
	gsi_safe_insert_before instead of gsi_insert_before.

	* gcc.dg/asan/pr112709-2.c: New test.