middle-end: Fix operation_could_trap_p for FIX_TRUNC expressions

middle-end: Fix operation_could_trap_p for FIX_TRUNC expressions

Floating-point to integer conversions can be inexact or invalid (e.g., due to
overflow or NaN).  However, since users of operation_could_trap_p infer the
bool FP_OPERATION argument from the expression's type, the FIX_TRUNC family
are considered non-trapping here.

This patch handles them explicitly.

gcc/ChangeLog:

	* tree-eh.cc (operation_could_trap_helper_p): Cover FIX_TRUNC
	expressions explicitly.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sve/pr96357.c: Change to avoid producing
	a conditional FIX_TRUNC_EXPR, whilst still reproducing the bug
	in PR96357.
	* gcc.dg/tree-ssa/ifcvt-fix-trunc-1.c: New test.
	* gcc.dg/tree-ssa/ifcvt-fix-trunc-2.c: Likewise.