LLVM provides a way of checking whether the constraints and the actual
inline assembly make sense. This commit introduces a check before
emitting code for the inline assembly. If LLVM rejects the inline
assembly (or its constraints), then the compiler emits an error E0668
("malformed inline assembly").
Signed-off-by: Levente Kurusa <lkurusa@acm.org>
(This is just the data structure changes and some boilerplate match
code that followed from it; the actual emission of these statements
comes in a follow-up commit.)
