Fix a couple places in docs where try_send wasn't changed to send_opt
std: Fix compiling on FreeBSD

Ah, the wonders of not being gated on FreeBSD...
Rewrite paragraph describing difference between try_send and send_opt
rustc: Ensure closures are "split-stack"

In upgrading LLVM, only rust functions had the "split-stack" attribute added.
This commit changes the addition of LLVM's "split-stack" attribute to *always*
occur and then we remove it sometimes if the "no_split_stack" rust attribute is
present.

Closes #13625
auto merge of #13628 : alexcrichton/rust/issue-13625, r=thestinger

In upgrading LLVM, only rust functions had the "split-stack" attribute added.
This commit changes the addition of LLVM's "split-stack" attribute to *always*
occur and then we remove it sometimes if the "no_split_stack" rust attribute is
present.

Closes #13625
auto merge of #13610 : jsanders/rust/sender-try-send-docs, r=alexcrichton

I was getting a bit confused by these and (I think) managed to track it down to fallout from #13448 and #13465.
auto merge of #13613 : alexcrichton/rust/fix-freebsd-compile, r=brson

Ah, the wonders of not being gated on FreeBSD...
Allow inheritance between structs.

No subtyping, no interaction with traits. Partially addresses #9912.
auto merge of #12562 : nick29581/rust/fields, r=nikomatsakis

No subtyping, no interaction with traits. Partially addresses #9912.