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/ui/missing-alloc_error_handler.rs

@@ -0,0 +1,33 @@
+// Copyright 2015 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-prefer-dynamic
+
+#![no_std]
+#![crate_type = "staticlib"]
+#![feature(panic_implementation, alloc_error_handler, alloc)]
+
+#[panic_implementation]
+fn panic(_: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+extern crate alloc;
+
+#[global_allocator]
+static A: MyAlloc = MyAlloc;
+
+struct MyAlloc;
+
+unsafe impl core::alloc::GlobalAlloc for MyAlloc {
+    unsafe fn alloc(&self, _: core::alloc::Layout) -> *mut u8 { 0 as _ }
+    unsafe fn dealloc(&self, _: *mut u8, _: core::alloc::Layout) {}
+}