librustc: Move inline asm stuff to different mod.
libsyntax: use a struct for inline asm in ast.
libsyntax: Allow selecting intel style asm.
librustc: add default per arch clobbers for asm.
librustc: remove already addressed XXX
auto merge of #5593 : luqmana/rust/inline-asm, r=catamorphism

Clean things up a bit. Also, allow selecting intel syntax in addition to the default AT&T dialect.