const-block: Add testcase

gcc/testsuite/ChangeLog:

	* rust/execute/torture/const_block1.rs: New test.

Author: CohenArthur

gcc/testsuite/rust/execute/torture/const_block1.rs

@@ -0,0 +1,9 @@
+const X: i32 = const {
+    let a = 15;
+    let b = 14;
+    a + b
+};
+
+fn main() -> i32 {
+    X - 29
+}