host lib: include <sys/types.h> for ssize_t

In uClibc neither <stdio.h> nor <strings.h> defines ssize_t.

Change-Id: I7fb6a0f51eae76062784952beb42298c486461b5
Signed-off-by: Alex Suykov <alex.suykov@gmail.com>
Reviewed-on: https://chromium-review.googlesource.com/320472
Commit-Ready: Stefan Reinauer <reinauer@google.com>
Tested-by: Stefan Reinauer <reinauer@google.com>
Reviewed-by: Stefan Reinauer <reinauer@google.com>