Add missing includes and external definitions

Add missing includes and external definitions

Several modules use std::array without including the
array header. Bad modules.

Some modules use STDOUT_FILENO and friends, or close()
without including unistd.h, where they are defined.

One module also uses WIFEXITED() without including
sys/wait.h.

Finally, environ is not specified to be defined in unistd.h. We
are required to define it ourselves according to POSIX, so let's
do that.