Put const eval check back.

Author: oxalica

clippy_tests/examples/range.rs

@@ -21,4 +21,7 @@ fn main() {
     let v2 = vec![4,5];
     let _x = v1.iter().zip(0..v1.len());
     let _y = v1.iter().zip(0..v2.len()); // No error
+
+    // check const eval
+    let _ = v1.iter().step_by(2/3);
 }

clippy_tests/examples/range.stderr

@@ -6,7 +6,15 @@ error: It is more idiomatic to use v1.iter().enumerate()
    |
    = note: `-D range-zip-with-len` implied by `-D warnings`
 
-error: aborting due to previous error
+error: Iterator::step_by(0) will panic at runtime
+  --> range.rs:26:13
+   |
+26 |     let _ = v1.iter().step_by(2/3);
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D iterator-step-by-zero` implied by `-D warnings`
+
+error: aborting due to 2 previous errors
 
 
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