unix: add flock(3C) support on Solaris

Fixes: golang/go#21410

Change-Id: Ie1971f7d6e0cfe405603e94c538a15dd5f467392
Reviewed-on: https://go-review.googlesource.com/55230
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/syscall_solaris.go

@@ -581,6 +581,7 @@ func IoctlGetTermio(fd int, req uint) (*Termio, error) {
 //sys	Fchown(fd int, uid int, gid int) (err error)
 //sys	Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error)
 //sys	Fdatasync(fd int) (err error)
+//sys Flock(fd int, how int) (err error)
 //sys	Fpathconf(fd int, name int) (val int, err error)
 //sys	Fstat(fd int, stat *Stat_t) (err error)
 //sys	Fstatvfs(fd int, vfsstat *Statvfs_t) (err error)

unix/zsyscall_solaris_amd64.go

@@ -43,6 +43,7 @@ import (
 //go:cgo_import_dynamic libc_fchown fchown "libc.so"
 //go:cgo_import_dynamic libc_fchownat fchownat "libc.so"
 //go:cgo_import_dynamic libc_fdatasync fdatasync "libc.so"
+//go:cgo_import_dynamic libc_flock flock "libc.so"
 //go:cgo_import_dynamic libc_fpathconf fpathconf "libc.so"
 //go:cgo_import_dynamic libc_fstat fstat "libc.so"
 //go:cgo_import_dynamic libc_fstatvfs fstatvfs "libc.so"
@@ -163,6 +164,7 @@ import (
 //go:linkname procFchown libc_fchown
 //go:linkname procFchownat libc_fchownat
 //go:linkname procFdatasync libc_fdatasync
+//go:linkname procFlock libc_flock
 //go:linkname procFpathconf libc_fpathconf
 //go:linkname procFstat libc_fstat
 //go:linkname procFstatvfs libc_fstatvfs
@@ -284,6 +286,7 @@ var (
 	procFchown,
 	procFchownat,
 	procFdatasync,
+	procFlock,
 	procFpathconf,
 	procFstat,
 	procFstatvfs,
@@ -702,6 +705,14 @@ func Fdatasync(fd int) (err error) {
 	return
 }
 
+func Flock(fd int, how int) (err error) {
+	_, _, e1 := sysvicall6(uintptr(unsafe.Pointer(&procFlock)), 2, uintptr(fd), uintptr(how), 0, 0, 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
 func Fpathconf(fd int, name int) (val int, err error) {
 	r0, _, e1 := sysvicall6(uintptr(unsafe.Pointer(&procFpathconf)), 2, uintptr(fd), uintptr(name), 0, 0, 0, 0)
 	val = int(r0)