Implement mknod and mknodat

src/header/sys_stat/mod.rs

src/platform/linux/mod.rs

src/platform/pal/mod.rs

src/platform/redox/mod.rs

tests/Makefile

tests/expected/bins_static/mkfifo.stderr

tests/expected/bins_static/mkfifo.stdout

tests/expected/bins_static/mknod.stderr

tests/expected/bins_static/mknod.stdout

tests/expected/bins_static/mknodat.stderr

tests/expected/bins_static/mknodat.stdout

tests/mkfifo.c

tests/mknod.c

tests/mknodat.c