Don't map thread stacks as MAP_SHARED (lol), fix i686 signal trampoline

See merge request redox-os/relibc!465

MAP_SHARED means it will continue to be shared after forks, which
obviously isn't the correct behavior. `acid thread` doesn't segfault
infinitely, anymore.

Implement the event queue ABI.

See merge request redox-os/relibc!454

Implement new low-level signal trampoline

See merge request redox-os/relibc!460

Fix thread spawning on aarch64

See merge request redox-os/relibc!463

* Correctly align the stack
* Fix argument order of the ldp instructions
* Remove unnecessary ldr x5 instruction

Add tests for further sys/resource.h constants

See merge request redox-os/relibc!462

Add stub for SIOCATMARK command of ioctl.

See merge request redox-os/relibc!461

Fix posix prio process (same as MR458 with fixed commits)

See merge request redox-os/relibc!459

Use standard casing and mangling for internal errno

See merge request redox-os/relibc!457

Add Crypt functions

See merge request redox-os/relibc!453

Use Cell representation for errno

See merge request redox-os/relibc!456

Panic when getpagesize() cannot succeed as specified

See merge request redox-os/relibc!455

Update rust-toolchain.toml

See merge request redox-os/relibc!452

This matches the version actually used by Redox OS. It also supports the
sparse index, which prevents having to clone the crates.io registry git
repo when rust-analyzer tries to run cargo metadata on relibc.

Scheme fmt

See merge request redox-os/relibc!451