Update rustc analyses to reflect asm! order-of-eval: outputs, then inputs.

Fix #14962.

Also reordered the fields in libsyntax to reflect the order that the
expressions occur in an instance of `asm!`, as an attempt to remind
others of this ordering.

Finally, added a couple notes about cases that may need to be further
revised when/if #14936 is addressed.
auto merge of #14966 : pnkfelix/rust/fsk-fix-asm-order-of-eval-issue-14962, r=alexcrichton

Fix #14962.

Update rustc analyses to reflect asm! order-of-eval: outputs, then inputs.

Also reordered the fields in libsyntax to reflect the order that the
expressions occur in an instance of `asm!`, as an attempt to remind
others of this ordering.

Finally, added a couple notes about cases that may need to be further
revised when/if #14936 is addressed.