unix: add Msync function on Solaris

Add the Msync function on solaris/amd64.

Change-Id: Idde0f9e693f924fef471acb42afb84e83c4cee76
Reviewed-on: https://go-review.googlesource.com/64370
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/unix/syscall_solaris.go b/unix/syscall_solaris.go
index dbb166e..76eade9 100644
--- a/unix/syscall_solaris.go
+++ b/unix/syscall_solaris.go
@@ -612,6 +612,7 @@
 //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	Nanosleep(time *Timespec, leftover *Timespec) (err error)