native, rustuv: Fix spawning with empty args

There was a bug in both libnative and libuv which prevented child processes from
being spawned correctly on windows when one of the arguments was an empty
string. The libuv bug has since been fixed upstream, and the libnative bug was
fixed as part of this commit.

When updating libuv, this also includes a fix for #15149.

Closes #15149
Closes #16272
libcore: Fix documentation comment for f32.
don't translate items when monomorphizing foreign-ABI functions
Make small doc contributions less onerous/intimidating
mk: Don't emit landing pads in stage 0.

Reduces time to build stage0 from 11:30 to 9:40 on my machine.
rust.md: Explicitly point out how special `'static` is.

Drive-by: fix description of `&content` to point out that `&'f type`
is (as of today) only for type expressions.
librustc: Don't use the same alloca for match binding which we reassign to in arm body.
librustc: Also use new alloca if matching on an arg or upvar which we reassign in the arm body.
librustc: Encode upvar_borrow_map in metadata.
removing 'str'='struct' search synonym

fixes #16384
rustdoc: use raw search in URL

fixes #16385
fixes #16271
auto merge of #16356 : ruud-v-a/rust/fix-f32-doc, r=steveklabnik

On a side note (but maybe this is not the right place to ask), the name `Float::two_pi` is inconsistent with `f32::consts::PI_2`.
auto merge of #16359 : epdtry/rust/mono-item-dedup-foreign, r=alexcrichton

Extend the changes from #16059 to the new generic foreign functions introduced by #15831.
auto merge of #16371 : Gankro/rust/friendly-contrib, r=brson

Had someone experience deep existential dread over building all of Rust on Windows just to do some minor fixes to the docs. This seems entirely unnecessary between reviewers + Bors for most purely english changes.
Fix misspelled comments for tests.
Fix typo
auto merge of #16373 : brson/rust/nopads, r=pcwalton

Reduces time to build stage0 from 11:30 to 9:40 on my machine.

There's a tradeoff here since doing this will make the stage1 compile-fail tests fail.

r? @pcwalton
auto merge of #16387 : Gankro/rust/doc-search, r=cmr

Fixes str/struct ambiguity (by removing the synonym) and pushes raw searches to the history instead of processed ones. 

# [Live Version Here](http://cg.scs.carleton.ca/~abeinges/doc/std/)
Fix typo `convering` to `converting`
auto merge of #16395 : superlogical/rust/patch-1, r=alexcrichton