Port NetBSD libc functions to Minix.

Port NetBSD libc functions to Minix.

This patch contains changes to NetBSD libc code base to make it
compile and work on Minix. Some of them are due to actual NetBSD
libc bugs, as we're compiling it in non-reentrant mode and with
a.out support, something not exactly frequent in NetBSD.
Others are proper fixes to port it to Minix (mostly sa_len
parameter missing in socket and a few mmap from files).