add test

Author: RalfJung

src/test/ui/consts/const-eval/issue-70723.rs

@@ -0,0 +1,5 @@
+#![feature(const_loop)]
+
+static _X: () = loop {}; //~ ERROR could not evaluate static initializer
+
+fn main() {}

src/test/ui/consts/const-eval/issue-70723.stderr

@@ -0,0 +1,9 @@
+error[E0080]: could not evaluate static initializer
+  --> $DIR/issue-70723.rs:3:17
+   |
+LL | static _X: () = loop {};
+   |                 ^^^^^^^ exceeded interpreter step limit (see `#[const_eval_limit]`)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.