fd445ddf96
builtin_macros: allow external consumers for AsmArgs parsing As discussed in Zulip (https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/parsing.20of.20AsmArgs.20for.20inline.20assembly), we need a function entry point that rustfmt can leverage from a pre-expansion context to get a more structured representation of the asm args without having to duplicate/maintain the token stream parsing r? ```@Amanieu``` and/or ```@joshtriplett```