internal-fn: Temporarily disable flag_trapv during .{ADD,SUB,MUL}_OVERFLOW...

internal-fn: Temporarily disable flag_trapv during .{ADD,SUB,MUL}_OVERFLOW etc. expansion [PR114753]

__builtin_{add,sub,mul}_overflow{,_p} builtins are well defined
for all inputs even for -ftrapv, and the -fsanitize=signed-integer-overflow
ifns shouldn't abort in libgcc but emit the desired ubsan diagnostics
or abort depending on -fsanitize* setting regardless of -ftrapv.
The expansion of these internal functions uses expand_expr* in various
places (e.g. MULT_EXPR at least in 2 spots), so temporarily disabling
flag_trapv in all those spots would be hard.
The following patch disables it around the bodies of 3 functions
which can do the expand_expr calls.
If it was in the C++ FE, I'd use some RAII sentinel, but I don't think
we have one in the middle-end.

2024-04-18  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/114753
	* internal-fn.cc (expand_mul_overflow): Save flag_trapv and
	temporarily clear it for the duration of the function, then
	restore previous value.
	(expand_vector_ubsan_overflow): Likewise.
	(expand_arith_overflow): Likewise.

	* gcc.dg/pr114753.c: New test.