(intentionally broken) add overflow checks to legacy RangeFrom

tests will fail, but this is meant for checking how it affects compile times, which shouldn't be impacted by the broken logic

Author: pitaj

library/core/src/iter/range.rs

@@ -1014,6 +1014,12 @@ impl<A: Step> Iterator for ops::RangeFrom<A> {
 
     #[inline]
     fn next(&mut self) -> Option<A> {
+        #[cfg(not(bootstrap))]
+        if crate::intrinsics::overflow_checks() {
+            self.start = Step::forward(self.start.clone(), 1);
+            return Some(self.start.clone());
+        }
+
         let n = Step::forward(self.start.clone(), 1);
         Some(mem::replace(&mut self.start, n))
     }
@@ -1025,6 +1031,13 @@ impl<A: Step> Iterator for ops::RangeFrom<A> {
 
     #[inline]
     fn nth(&mut self, n: usize) -> Option<A> {
+        #[cfg(not(bootstrap))]
+        if crate::intrinsics::overflow_checks() {
+            let plus_n = Step::forward(self.start.clone(), n);
+            self.start = Step::forward(plus_n.clone(), 1);
+            return Some(self.start.clone());
+        }
+
         let plus_n = Step::forward(self.start.clone(), n);
         self.start = Step::forward(plus_n.clone(), 1);
         Some(plus_n)