Upgrade LLVM for segmented stacks on thumb

This updates the LLVM submodule to the `rust-llvm-2014-02-19` tag which is the
old one with https://github.com/rust-lang/llvm/pull/4 cherry-picked on top.

Awesome job by @neykov for this!
Update comments in the prelude

The comments say that the prelude imports std::io::println since it would
be annoying to have to import it in every program that uses it. However,
the prelude doesn't actually import that function anymore. So, update the
comments to better match reality.
move enum_set to libcollections. #8784
Changed NonCamelCaseTypes lint to warn by default

Added allow(non_camel_case_types) to librustc where necesary

Tried to fix problems with non_camel_case_types outside rustc

fixed failing tests

Docs updated

Moved #[allow(non_camel_case_types)] a level higher.

markdown.rs reverted

Fixed timer that was failing tests

Fixed another timer
auto merge of #12407 : alexcrichton/rust/up-llvm, r=sfackler

This updates the LLVM submodule to the `rust-llvm-2014-02-19` tag which is the
old one with https://github.com/rust-lang/llvm/pull/4 cherry-picked on top.

Awesome job by @neykov for this!
auto merge of #12290 : mrshu/rust/lint-warn-by-default, r=alexcrichton

This first part of my attempts to fix #11432.

In this one I only set NonCamelCaseTypes to warn by default and tried to fix errors that were reported by `make check`.

Please feel free to let me know if I missed something or didn't do it the right way.

Thanks.
auto merge of #12410 : DaGenix/rust/fix-incorrect-comment, r=alexcrichton

The comments say that the prelude imports std::io::println since it would
be annoying to have to import it in every program that uses it. However,
the prelude doesn't actually import that function anymore. So, update the
comments to better match reality.
auto merge of #12415 : HeroesGrave/rust/move-enum-set, r=alexcrichton

Part of #8784

Also removed the one glob import.