Fix regression caused by M2libc's fb6701a73189afca152ea1154650c315df4e6a93 commit

Fix a typo in a comment.

Set OPERATING_SYSTEM=Linux environmental variable.

Add M2libc/stdio.h to build sources.

Merge branch 'typo' of https://github.com/stikonas/stage0-posix-aarch64

Fix a missing quotation mark.

Breaking change in M2libc v0.2.1

Fix a typo.

Fix a typo.

Fix comments.

Set TMPDIR for systems without /tmp

Fix regression

Broke out AArch64

Update M2libc.

This also needs some adjustment to build scripts.
fcntl.h has to be built before stdlib.c.

riscv32: add kaem scripts.

Clean up the bits that were not adjusted following live-bootstrap
unification work

Move kaem.aarch64 to top directory for better live-bootstrap integration

convert AArch64 hex2 to use stack for read/write syscalls to speed up qemu performance

Move kaem.x86 to top directory for better live-bootstrap integration

Put all build artifacts in artifact and isolate the riscv64 build and output