Added some constants in linux for file modes in the new branch

cbindgen

include/bits/signal.h

src/fcntl/src/lib.rs

src/fcntl/src/linux.rs

src/fcntl/src/redox.rs

src/signal/cbindgen.toml

src/signal/src/lib.rs

src/signal/src/linux.rs

src/signal/src/redox.rs

src/string/src/lib.rs

src/wait/cbindgen.toml

tests/Makefile

tests/expected/string/strpbrk.stderr

tests/expected/string/strpbrk.stdout

tests/expected/string/strstr.stderr

tests/expected/string/strstr.stdout

tests/string/strpbrk.c

tests/string/strstr.c