Add regression test

Author: oli-obk

tests/codegen/const_scalar_pair.rs

@@ -0,0 +1,10 @@
+// compile-flags: --crate-type=lib -Copt-level=0 -Zmir-opt-level=0 -C debuginfo=2
+
+// CHECK: @0 = private unnamed_addr constant <{ [8 x i8] }> <{ [8 x i8] c"\01\00\00\00\02\00\00\00" }>, align 4
+
+#![feature(inline_const)]
+
+pub fn foo() -> (i32, i32) {
+    // CHECK: %0 = load i32, ptr @0, align 4
+    const { (1, 2) }
+}