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_darwin.go

@@ -292,12 +292,6 @@ func IoctlGetTermios(fd int, req uint) (*Termios, error) {
 //sys	Mkdirat(dirfd int, 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	Msync(b []byte, flags int) (err error)
-//sys	Munlock(b []byte) (err error)
-//sys	Munlockall() (err error)
 //sys	Open(path string, mode int, perm uint32) (fd int, err error)
 //sys	Openat(dirfd int, path string, mode int, perm uint32) (fd int, err error)
 //sys	Pathconf(path string, name int) (val int, err error)
@@ -374,9 +368,6 @@ func IoctlGetTermios(fd int, req uint) (*Termios, error) {
 // Add_profil
 // Kdebug_trace
 // Sigreturn
-// Mmap
-// Mlock
-// Munlock
 // Atsocket
 // Kqueue_from_portset_np
 // Kqueue_portset
@@ -469,8 +460,6 @@ func IoctlGetTermios(fd int, req uint) (*Termios, error) {
 // Lio_listio
 // __pthread_cond_wait
 // Iopolicysys
-// Mlockall
-// Munlockall
 // __pthread_kill
 // __pthread_sigmask
 // __sigwait