unix: export sizeof consts

Export the sizeof(Ptr|Short|Int|Long|LongLong) consts. This allows users
to get this information (e.g. for alignment purposes) without using cgo
or generating these constants themselves.

Change-Id: I8640482bf67b89c2f2b6e9a116ba7bc268f8135a
Reviewed-on: https://go-review.googlesource.com/c/139617
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/unix/types_dragonfly.go b/unix/types_dragonfly.go
index 386d5f8..3365dd7 100644
--- a/unix/types_dragonfly.go
+++ b/unix/types_dragonfly.go
@@ -65,14 +65,14 @@
 */
 import "C"
 
-// Machine characteristics; for internal use.
+// Machine characteristics
 
 const (
-	sizeofPtr      = C.sizeofPtr
-	sizeofShort    = C.sizeof_short
-	sizeofInt      = C.sizeof_int
-	sizeofLong     = C.sizeof_long
-	sizeofLongLong = C.sizeof_longlong
+	SizeofPtr      = C.sizeofPtr
+	SizeofShort    = C.sizeof_short
+	SizeofInt      = C.sizeof_int
+	SizeofLong     = C.sizeof_long
+	SizeofLongLong = C.sizeof_longlong
 )
 
 // Basic types