std: Move the bitflags! macro to a gated crate

In accordance with [collections reform part 2][rfc] this macro has been moved to
an external [bitflags crate][crate] which is [available though
crates.io][cratesio]. Inside the standard distribution the macro has been moved
to a crate called `rustc_bitflags` for current users to continue using.

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0509-collections-reform-part-2.md
[crate]: https://github.com/rust-lang/bitflags
[cratesio]: http://crates.io/crates/bitflags

The major user of `bitflags!` in terms of a public-facing possibly-stable API
today is the `FilePermissions` structure inside of `std::io`. This user,
however, will likely no longer use `bitflags!` after I/O reform has landed. To
prevent breaking APIs today, this structure remains as-is.

Current users of the `bitflags!` macro should add this to their `Cargo.toml`:

    bitflags = "0.1"

and this to their crate root:

    #[macro_use] extern crate bitflags;

Due to the removal of a public macro, this is a:

[breaking-change]

src/librustc/lib.rs

@@ -44,6 +44,7 @@ extern crate rbml;
 extern crate collections;
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;
+#[macro_use] #[no_link] extern crate rustc_bitflags;
 
 extern crate "serialize" as rustc_serialize; // used by deriving
 

src/librustc_bitflags/lib.rs

@@ -8,10 +8,16 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![crate_name = "rustc_bitflags"]
 #![unstable]
+#![staged_api]
+#![crate_type = "rlib"]
+#![no_std]
 
 //! A typesafe bitmask flag generator.
 
+#[cfg(test)] #[macro_use] extern crate std;
+
 /// The `bitflags!` macro generates a `struct` that holds a set of C-style
 /// bitmask flags. It is useful for creating typesafe wrappers for C APIs.
 ///
@@ -21,6 +27,8 @@
 /// # Example
 ///
 /// ```{.rust}
+/// #[macro_use] extern crate rustc_bitflags;
+///
 /// bitflags! {
 ///     flags Flags: u32 {
 ///         const FLAG_A       = 0b00000001,
@@ -45,6 +53,8 @@
 /// The generated `struct`s can also be extended with type and trait implementations:
 ///
 /// ```{.rust}
+/// #[macro_use] extern crate rustc_bitflags;
+///
 /// use std::fmt;
 ///
 /// bitflags! {
@@ -273,8 +283,8 @@ macro_rules! bitflags {
 #[cfg(test)]
 #[allow(non_upper_case_globals)]
 mod tests {
-    use hash::{self, SipHasher};
-    use option::Option::{Some, None};
+    use std::hash::{self, SipHasher};
+    use std::option::Option::{Some, None};
 
     bitflags! {
         #[doc = "> The first principle is that you must not fool yourself — and"]

src/librustc_llvm/lib.rs

@@ -28,6 +28,7 @@
 #![allow(unknown_features)] #![feature(int_uint)]
 
 extern crate libc;
+#[macro_use] #[no_link] extern crate rustc_bitflags;
 
 pub use self::OtherAttribute::*;
 pub use self::SpecialAttribute::*;

src/librustc_resolve/lib.rs

@@ -23,6 +23,7 @@
 
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;
+#[macro_use] #[no_link] extern crate rustc_bitflags;
 
 extern crate rustc;
 

src/libstd/lib.rs

@@ -111,7 +111,7 @@
 #![feature(box_syntax)]
 #![feature(old_impl_check)]
 #![feature(optin_builtin_traits)]
-#![allow(unknown_features)] #![feature(int_uint)]
+#![feature(int_uint)]
 
 // Don't link to std. We are std.
 #![no_std]
@@ -136,6 +136,8 @@ extern crate alloc;
 extern crate unicode;
 extern crate libc;
 
+#[macro_use] #[no_link] extern crate rustc_bitflags;
+
 // Make std testable by not duplicating lang items. See #2912
 #[cfg(test)] extern crate "std" as realstd;
 #[cfg(test)] pub use realstd::marker;
@@ -181,9 +183,6 @@ pub use unicode::char;
 #[macro_use]
 mod macros;
 
-#[macro_use]
-pub mod bitflags;
-
 mod rtdeps;
 
 /* The Prelude. */

src/libsyntax/lib.rs

@@ -35,6 +35,7 @@ extern crate serialize;
 extern crate term;
 extern crate libc;
 #[macro_use] extern crate log;
+#[macro_use] #[no_link] extern crate rustc_bitflags;
 
 extern crate "serialize" as rustc_serialize; // used by deriving