[PATCH] devel/devhelp buildlink3 file

[Dan Cîrnaț <dan%alt.md@localhost>]

devel/devhelp lacks a buildlink3.mk file. Providing one would allow
packaging software that depends on libdevhelp, i.e. gnome-builder

Example buildlink3 file that I tested:

Index: devel/devhelp/buildlink3.mk
===================================================================
RCS file: devel/devhelp/buildlink3.mk
diff -N devel/devhelp/buildlink3.mk
--- /dev/null   1 Jan 1970 00:00:00 -0000
+++ devel/devhelp/buildlink3.mk 31 May 2020 18:53:03 -0000
@@ -0,0 +1,13 @@
+# $NetBSD$
+
+BUILDLINK_TREE+=       devhelp
+
+.if !defined(DEVHELP_BUILDLINK3_MK)
+DEVHELP_BUILDLINK3_MK:=
+
+BUILDLINK_API_DEPENDS.devhelp+=        devhelp>=3.34.0nb3
+BUILDLINK_PKGSRCDIR.devhelp?=  ../../devel/devhelp
+
+.endif # DEVHELP_BUILDLINK3_MK
+
+BUILDLINK_TREE+=       -devhelp