Rollup merge of #128666 - pitaj:intrinsic-overflow_checks, r=BoxyUwU

Add `overflow_checks` intrinsic

This adds an intrinsic which allows code in a pre-built library to inherit the overflow checks option from a crate depending on it. This enables code in the standard library to explicitly change behavior based on whether `overflow_checks` are enabled, regardless of the setting used when standard library was compiled.

This is very similar to the `ub_checks` intrinsic, and refactors the two to use a common mechanism.

The primary use case for this is to allow the new `RangeFrom` iterator to yield the maximum element before overflowing, as requested [here](rust-lang/rust#125687 (comment)). This PR includes a working `IterRangeFrom` implementation based on this new intrinsic that exhibits the desired behavior.

[Prior discussion on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Ability.20to.20select.20code.20based.20on.20.60overflow_checks.60.3F)

Author: Zalathar

src/base.rs

@@ -865,17 +865,8 @@ fn codegen_stmt<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, cur_block: Block, stmt:
                                 fields.iter(),
                             )
                             .bytes(),
-                        NullOp::UbChecks => {
-                            let val = fx.tcx.sess.ub_checks();
-                            let val = CValue::by_val(
-                                fx.bcx.ins().iconst(types::I8, i64::from(val)),
-                                fx.layout_of(fx.tcx.types.bool),
-                            );
-                            lval.write_cvalue(fx, val);
-                            return;
-                        }
-                        NullOp::ContractChecks => {
-                            let val = fx.tcx.sess.contract_checks();
+                        NullOp::RuntimeChecks(kind) => {
+                            let val = kind.value(fx.tcx.sess);
                             let val = CValue::by_val(
                                 fx.bcx.ins().iconst(types::I8, i64::from(val)),
                                 fx.layout_of(fx.tcx.types.bool),