Tweak implementation of overflow checking assertions

Extract and reuse logic controlling behaviour of overflow checking
assertions instead of duplicating it three times.

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -155,7 +155,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
 
     /// Whether Assert(OverflowNeg) and Assert(Overflow) MIR terminators should actually
     /// check for overflow.
-    fn ignore_checkable_overflow_assertions(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
+    fn ignore_optional_overflow_checks(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
 
     /// Entry point for obtaining the MIR of anything that should get evaluated.
     /// So not just functions and shims, but also const/static initializers, anonymous
@@ -474,7 +474,7 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
     }
 
     #[inline(always)]
-    fn ignore_checkable_overflow_assertions(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
+    fn ignore_optional_overflow_checks(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
         false
     }