Make const_eval_select a real intrinsic

library/core/src/str/mod.rs

@@ -91,10 +91,12 @@ const fn slice_error_fail(s: &str, begin: usize, end: usize) -> ! {
     }
 }
 
+#[track_caller]
 const fn slice_error_fail_ct(_: &str, _: usize, _: usize) -> ! {
     panic!("failed to slice string");
 }
 
+#[track_caller]
 fn slice_error_fail_rt(s: &str, begin: usize, end: usize) -> ! {
     const MAX_DISPLAY_LENGTH: usize = 256;
     let trunc_len = s.floor_char_boundary(MAX_DISPLAY_LENGTH);