Only build net/hook_cloexec.go on GNU/Linux and FreeBSD, because those
are the only systems with accept4.
Add syscall/libcall_bsd.go to define sendfile for *BSD and Solaris.
Revert tcpsockopt_solaris.go back to the earlier version, so that it
works on Solaris 10.
Always pass the address of a Pid_t value to TIOCGPGRP and TIOCSPGRP.
Include <unistd.h> in runtime/go-varargs.c.
Reviewed-on: https://go-review.googlesource.com/16719
From-SVN: r229880
PR go/67874
net, runtime: Call C library fcntl function rather than syscall.Syscall.
Not all systems define a fcntl syscall; some only have fcntl64.
Fixes GCC PR go/67874.
Reviewed-on: https://go-review.googlesource.com/15497
From-SVN: r228576
