Teach rustc about DW_AT_noreturn and a few more DIFlags

src/test/codegen/noreturnflag.rs

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+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-tidy-linelength
+// min-llvm-version 3.8
+
+// compile-flags: -g -C no-prepopulate-passes
+
+// CHECK-LABEL: foo
+// CHECK: {{.*}}DISubprogram{{.*}} name: "foo",{{.*}}DIFlagNoReturn{{.*}}
+
+#[no_mangle]
+pub fn foo() -> ! {
+    loop {}
+}
+
+// CHECK-LABEL: main
+// CHECK: {{.*}}DISubprogram{{.*}}name: "main",{{.*}}DIFlagMainSubprogram{{.*}}
+
+pub fn main() {
+    foo();
+}