doc/guide-ffi: A few minor typo/language fixes

Signed-off-by: Anton Lofgren <alofgren@op5.com>
Guide: match
Guide: looping
Guide: Standard input
Convert a first batch of diagnostics to have error codes
glob::MatchOptions struct fields should be public
Document that Result.unwrap prints the Err's value

It is implied by the Show bound, but that implication can be missed.
auto merge of #15632 : masklinn/rust/patch-1, r=alexcrichton

I saw that it was bounded by `Show` but the implication is no guarantee (and had only 0.10 to test, where this behavior has been added to 0.11)
auto merge of #15655 : lightsofapollo/rust/glob-match-options-pub, r=alexcrichton

Not sure how to test this correctly I assume the current tests pass now because of the crate boundaries [and that this is fallout from private by default]?
doc: missing quote in keyword Send
auto merge of #15666 : yorkie/rust/patch-1, r=alexcrichton
Move llvm bindings to their own crate
Extract librustc_back from librustc
rustc: Invert some rpath dependencies
Extract rpath to rustc_back::rpath
rustc: Invert some archive deps
rustc: Move ArchiveRO to rustc_llvm

It is a wrapper around LLVM.
rustc: Move archive to rustc_back
rustc_back: Update crate docs

Indicate that anything that can be extracted here should and that things with
syntax deps should be split out someday.
rustc: Move util::fs to rustc_back