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
make rustdoc more responsive

* move some sidebar contents to a title bar when small
* inline description toggle when small
* make out-of-band and in-band content share space, rather than float and clash
* compress wording of out-of-band content to avoid line-wrap as much as possible
libcollections: Fix RingBuf growth for non-power-of-two capacities
windows: Fix several tests on 64-bit.

Signed-off-by: Peter Atashian <retep998@gmail.com>
rustc: gensym the module names for --test to avoid introducing user-accessible names.

This requires avoiding `quote_...!` for constructing the parts of the
__test module, since that stringifies and reinterns the idents, losing
the special gensym'd nature of them. (#15962.)
Guide: strings
windows: Fix INVALID_HANDLE_VALUE
Made INVALID_HANDLE_VALUE actually a HANDLE.
Removed all useless casts during INVALID_HANDLE_VALUE comparisons.

Signed-off-by: Peter Atashian <retep998@gmail.com>
enable PIE by default on Linux for full ASLR

Rust already builds all code as position independent by default, so the
linker can be told to build a position independent executable if it's
not disabled with `-C relocation-model=dynamic-no-pic`. Position
independent code does have a significant cost on i686 (not on x86_64 or
ARM) but there's no significant cost to linking code that's already
position independent as a position independent executable.

Address space layout randomization makes exploiting vulnerabilities much
more difficult by providing a statistical defence against an attempt to
find or modify existing code / data. Without ASLR, it's trivial to use a
vulnerability to take over control of the process via return-oriented
programming.

Rust code can be used for return-oriented programming whether it is safe
or unsafe, so even a fully safe application needs to be built as a
position independent executable to defend against vulnerabilities in
unsafe blocks or C libraries.

Sample program:

    extern crate libc;

    use std::mem;

    static mut global: u32 = 5;
    static constant: u32 = 5;
    fn foo() {}

    fn main() {
        let local = 5;
        println!("stack: {}, global: {}, constant: {}, fn: {}, lib fn: {}",
                 &local as *const u32,
                 unsafe { &global as *const u32 },
                 &constant as *const u32,
                 unsafe { mem::transmute::<_, *const ()>(foo) },
                 unsafe { mem::transmute::<_, *const ()>(libc::mprotect) });
    }

Before:

    stack: 0x3ff15eb9f94, global: 0x6ab488, constant: 0x47db40, fn: 0x4030e0, lib fn: 0x32749547530
    stack: 0x3b5d47d80e4, global: 0x6ab488, constant: 0x47db40, fn: 0x4030e0, lib fn: 0x394469a7530
    stack: 0x3fe2c4e5564, global: 0x6ab488, constant: 0x47db40, fn: 0x4030e0, lib fn: 0x399734a2530
    stack: 0x3e525e0fb24, global: 0x6ab488, constant: 0x47db40, fn: 0x4030e0, lib fn: 0x2f62a810530
    stack: 0x3b50fb3eae4, global: 0x6ab488, constant: 0x47db40, fn: 0x4030e0, lib fn: 0x2e590e86530

After:

    stack: 0x38cf12c90a4, global: 0x3e2d46b488, constant: 0x3e2d23cf80, fn: 0x3e2d1c2510, lib fn: 0x2617d3b4530
    stack: 0x3d733faf474, global: 0x7eb1839488, constant: 0x7eb160af80, fn: 0x7eb1590510, lib fn: 0x32d30c1f530
    stack: 0x3bb42212ec4, global: 0x5bbb365488, constant: 0x5bbb136f80, fn: 0x5bbb0bc510, lib fn: 0x3595e6c1530
    stack: 0x39f678c1ab4, global: 0x22c4e3c488, constant: 0x22c4c0df80, fn: 0x22c4b93510, lib fn: 0x3835b727530
    stack: 0x3afb25bd394, global: 0x493eab2488, constant: 0x493e883f80, fn: 0x493e809510, lib fn: 0x3478d6a7530

This may also be necessary on other platforms, but I can only test on
Linux right now. Note that GDB gained support for debugging position
independent executables in version 7.1 (March 2010).
rustdoc: Set a nonzero exit status on failure

Now that rustdoc is spawning a child task, the program won't exit with a default
error code if the main task fails (because it never fails). This commit forces
the main task to wait for a child task in order to correctly propagate failure.

Closes #16341
Implement Win64 system ABI.
Move system header includes above valgrind.h include

This allows rustc to be build under msys2's mingw64 gcc
Adding test for issue #15917 which was previously fixed with #15709
libcore: Fix documentation comment for f32.
auto merge of #16333 : steveklabnik/rust/guide_strings, r=brson

I _think_ this is the right place to introduce strings. It's a bit hard to talk about without understanding pointers and ownership, but you need to have some idea of what's going on...
don't translate items when monomorphizing foreign-ABI functions
auto merge of #16336 : retep998/rust/master, r=brson

Several of the tests in `make check-fast` were failing so this fixes those tests.
auto merge of #16277 : Gankro/rust/responsive-docs, r=cmr

* move some sidebar contents to a title bar when small
* inline description toggle when small
* make out-of-band and in-band content share space, rather than float and clash
* compress wording of out-of-band content to avoid line-wrap as much as possible

## [Live Version Here](http://cg.scs.carleton.ca/~abeinges/doc/index.html)

Pages Of Interest:
* [Vec](http://cg.scs.carleton.ca/~abeinges/doc/std/vec/struct.Vec.html) (small path)
* [TreeSet](http://cg.scs.carleton.ca/~abeinges/doc/collections/treemap/struct.TreeSet.html) (long path)
* [std](http://cg.scs.carleton.ca/~abeinges/doc/std/index.html) (for stability dash)

TBD in a future PR is to convert links in the sidebar into a series of nest ul/li's, so that they can easily be moved to a drop-down in the new title bar. I think this is out of scope for this PR, but am willing to implement it now if desired.
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.
auto merge of #16314 : Ryman/rust/ringbuf_non_pow2, r=huonw

See test for details.