rustc: Use rust strings for failure arguments

This avoids having to perform conversions from `*u8` to `&'static str` which can
suck in a good deal of code.

Closes #14442

src/test/auxiliary/lang-item-public.rs

@@ -11,7 +11,7 @@
 #![no_std]
 
 #[lang="fail_"]
-fn fail(_: *i8, _: *i8, _: uint) -> ! { loop {} }
+fn fail(_: &'static str, _: &'static str, _: uint) -> ! { loop {} }
 
 #[lang = "stack_exhausted"]
 extern fn stack_exhausted() {}