Make sure all the asm! invocations are volatile

[farcaller]

llvm seems to toss around the assembly block unless it's volatile. Given that all asm! blocks must execute at the code point where they are defined, they all should be marked volatile.

[bgamari]

A very good point; this affected lock in #11

[bharrisau]

Loadable lints are coming in, so we can probably make one for this (I'm also thinking we have one for out of date TODOs).

[bharrisau]

note for me: rust-lang/rust#15024