Fix stat stack corruption and link test

src/arpainet/src/lib.rs

src/platform/src/lib.rs

src/platform/src/linux/mod.rs

src/platform/src/redox/mod.rs

src/platform/src/types.rs

src/signal/src/lib.rs

src/sys_socket/src/lib.rs

src/sys_stat/src/lib.rs

src/sys_utsname/src/lib.rs

tests/.gitignore

tests/Makefile

tests/expected/unistd/stat.stderr

tests/expected/unistd/stat.stdout

tests/unistd/link.c

tests/unistd/stat.c

tests/unistd/unlink.c