Update to new system calls and enviromental variables

.gitmodules

src/liblibc

src/libstd/sys/redox/mod.rs

src/libstd/sys/redox/os.rs

src/libstd/sys/redox/process.rs

src/libstd/sys/redox/syscall/call.rs

src/libstd/sys/redox/syscall/flag.rs

src/libstd/sys/redox/syscall/number.rs