Implement #[alloc_error_handler]

This to-be-stable attribute is equivalent to `#[lang = "oom"]`.
It is required when using the alloc crate without the std crate.
It is called by `handle_alloc_error`, which is in turned called
by "infallible" allocations APIs such as `Vec::push`.

src/test/compile-fail/alloc-error-handler-bad-signature-1.rs

@@ -0,0 +1,28 @@
+// Copyright 2018 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.
+
+// compile-flags:-C panic=abort
+
+#![feature(alloc_error_handler, panic_implementation)]
+#![no_std]
+#![no_main]
+
+use core::alloc::Layout;
+
+#[alloc_error_handler]
+fn oom(
+    info: &Layout, //~ ERROR argument should be `Layout`
+) -> () //~ ERROR return type should be `!`
+{
+    loop {}
+}
+
+#[panic_implementation]
+fn panic(_: &core::panic::PanicInfo) -> ! { loop {} }

src/test/compile-fail/alloc-error-handler-bad-signature-2.rs

@@ -0,0 +1,27 @@
+// Copyright 2018 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.
+
+// compile-flags:-C panic=abort
+
+#![feature(alloc_error_handler, panic_implementation)]
+#![no_std]
+#![no_main]
+
+struct Layout;
+
+#[alloc_error_handler]
+fn oom(
+    info: Layout, //~ ERROR argument should be `Layout`
+) { //~ ERROR return type should be `!`
+    loop {}
+}
+
+#[panic_implementation]
+fn panic(_: &core::panic::PanicInfo) -> ! { loop {} }

src/test/compile-fail/alloc-error-handler-bad-signature-3.rs

@@ -0,0 +1,25 @@
+// Copyright 2018 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.
+
+// compile-flags:-C panic=abort
+
+#![feature(alloc_error_handler, panic_implementation)]
+#![no_std]
+#![no_main]
+
+struct Layout;
+
+#[alloc_error_handler]
+fn oom() -> ! { //~ ERROR function should have one argument
+    loop {}
+}
+
+#[panic_implementation]
+fn panic(_: &core::panic::PanicInfo) -> ! { loop {} }

src/test/compile-fail/feature-gate-alloc-error-handler.rs

@@ -0,0 +1,21 @@
+// Copyright 2018 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.
+
+// compile-flags:-C panic=abort
+
+#![no_std]
+#![no_main]
+
+use core::alloc::Layout;
+
+#[alloc_error_handler] //~ ERROR #[alloc_error_handler] is an unstable feature (see issue #51540)
+fn oom(info: Layout) -> ! {
+    loop {}
+}