add cfg kani

Author: thanhnguyen-aws

library/core/src/slice/memchr.rs

@@ -2,6 +2,7 @@
 // Copyright 2015 Andrew Gallant, bluss and Nicolas Koch
 
 use crate::intrinsics::const_eval_select;
+#[cfg(kani)]
 use crate::kani;
 
 const LO_USIZE: usize = usize::repeat_u8(0x01);