Adds atomic_load, atomic_load_acq, atomic_store, and atomic_store_rel intrinsics.
The default versions (atomic_load and atomic_store) are sequentially consistent.
The atomic_load_acq intrinsic acquires as described in [1].
The atomic_store_rel intrinsic releases as described in [1].

[1]: http://llvm.org/docs/Atomics.html
Removed unnecessary check from build.rs
Correct #[always_inline] -> #[inline(always)] and __attribute((...)) -> __attribute__((...)).
auto merge of #6447 : luqmana/rust/6446, r=thestinger

#6446
doc: document the #[deriving] attribute.

Closes #4916.
auto merge of #6448 : huonw/rust/deriving-doc, r=Aatch

Closes #4916.
Tidy
auto merge of #6437 : Thiez/rust/atomic, r=Aatch

This pull request adds 4 atomic intrinsics to the compiler, in preparation for #5042.

* `atomic_load(src: &int) -> int` performs an atomic sequentially consistent load.
* `atomic_load_acq(src: &int) -> int` performs an atomic acquiring load.
* `atomic_store(dst: &mut int, val: int)` performs an atomic sequentially consistent store.
* `atomic_store_rel(dst: &mut int, val: int)` performs an atomic releasing store.

For more information about the whole acquire/release thing: http://llvm.org/docs/Atomics.html

r?