Allow panicking with string literal messages inside constants

src/test/ui/issues/issue-32829.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 static S : u64 = { { panic!("foo"); 0 } };
-//~^ ERROR calls in statics are limited
+//~^ ERROR panicking in statics is unstable
 
 fn main() {
     println!("{:?}", S);

src/test/ui/issues/issue-32829.stderr

@@ -1,11 +1,12 @@
-error[E0015]: calls in statics are limited to constant functions, tuple structs and tuple variants
+error[E0658]: panicking in statics is unstable (see issue #51999)
   --> $DIR/issue-32829.rs:11:22
    |
 LL | static S : u64 = { { panic!("foo"); 0 } };
    |                      ^^^^^^^^^^^^^^
    |
+   = help: add #![feature(const_panic)] to the crate attributes to enable
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0015`.
+For more information about this error, try `rustc --explain E0658`.