Use $crate and macro reexport to reduce duplicated code

Many of libstd's macros are now re-exported from libcore and libcollections.
Their libstd definitions have moved to a macros_stage0 module and can disappear
after the next snapshot.

Where the two crates had already diverged, I took the libstd versions as
they're generally newer and better-tested. See e.g. d3c831b, which was a fix to
libstd's assert_eq!() that didn't make it into libcore's.

Fixes #16806.

src/test/run-pass/vec-macro-no-std.rs

@@ -0,0 +1,39 @@
+// Copyright 2014 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.
+
+#![feature(phase, lang_items)]
+#![no_std]
+
+#[phase(plugin, link)]
+extern crate core;
+extern crate libc;
+
+#[phase(plugin, link)]
+extern crate collections;
+
+use core::option::Option::Some;
+use core::slice::SliceExt;
+use collections::vec::Vec;
+
+#[lang = "stack_exhausted"] extern fn stack_exhausted() {}
+#[lang = "eh_personality"] extern fn eh_personality() {}
+#[lang = "panic_fmt"] fn panic_fmt() -> ! { loop {} }
+
+// Issue #16806
+
+#[start]
+fn start(_argc: int, _argv: *const *const u8) -> int {
+    let x: Vec<u8> = vec![0, 1, 2];
+    match x.last() {
+        Some(&2) => (),
+        _ => panic!(),
+    }
+    0
+}