* fix return types
* fix type casts on returns

wait and waitpid

Implement strstr() and strpbrk() from string.h

Update cbindgen and fix issues with signal

The sigaction struct should not be a typedef, but the sigset_t struct
should be a typedef.

Update cbindgen to parse modules with a path attribute and revert the
following commits:
 - 996fad70.
 - cfe98ab3.

Actual working tests on strspn and strcspn

Yet another fix for strcspn and strspn.

Add the no_mangle attribute to fns

Add the no_mangle attribute to functions without it.

Change the type of byteset from [u8] to [usize] in strcspn and strspn. Hopefully this is the last bug in these!

Add missing extern crate statements

Add missing extern crate statements.