unix: unify memory functions on BSD

Make Madvice, Mlock, Mlockall, Mprotect, Msync, Munlock and Munlockall
available equally on all BSD flavors. NetBSD was previously lacking
SYS_MSYNC, so add it.

Reorder the //sys function prototype alphabetically and clean up already
implemented syscalls everywhere.

Also add tests for Mprotect, Msync and Madvice - now that they're
available on all unix platforms.

Fixes golang/go#18513

Change-Id: I0eb502d72c7e991f191fb96225ef04e8297d8b8d
Reviewed-on: https://go-review.googlesource.com/56172
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/syscall_dragonfly.go

@@ -174,11 +174,6 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, err error) {
 //sys	Mkdir(path string, mode uint32) (err error)
 //sys	Mkfifo(path string, mode uint32) (err error)
 //sys	Mknod(path string, mode uint32, dev int) (err error)
-//sys	Mlock(b []byte) (err error)
-//sys	Mlockall(flags int) (err error)
-//sys	Mprotect(b []byte, prot int) (err error)
-//sys	Munlock(b []byte) (err error)
-//sys	Munlockall() (err error)
 //sys	Nanosleep(time *Timespec, leftover *Timespec) (err error)
 //sys	Open(path string, mode int, perm uint32) (fd int, err error)
 //sys	Pathconf(path string, name int) (val int, err error)
@@ -253,9 +248,6 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, err error) {
 // Add_profil
 // Kdebug_trace
 // Sigreturn
-// Mmap
-// Mlock
-// Munlock
 // Atsocket
 // Kqueue_from_portset_np
 // Kqueue_portset
@@ -348,8 +340,6 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, err error) {
 // Lio_listio
 // __pthread_cond_wait
 // Iopolicysys
-// Mlockall
-// Munlockall
 // __pthread_kill
 // __pthread_sigmask
 // __sigwait
@@ -402,7 +392,6 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, err error) {
 // Sendmsg_nocancel
 // Recvfrom_nocancel
 // Accept_nocancel
-// Msync_nocancel
 // Fcntl_nocancel
 // Select_nocancel
 // Fsync_nocancel