debian/changelog

+libglvnd (1.3.0-7) unstable; urgency=medium
+
+  * control: Add libglx-dev to libgl-dev Depends.
+
+ -- Timo Aaltonen <tjaalton@debian.org>  Wed, 08 Jan 2020 14:11:25 +0200
+
 libglvnd (1.3.0-6) unstable; urgency=medium
 
   * Move glx headers to libglx-dev. (Closes: #947364)

debian/control

@@ -172,6 +172,7 @@ Package: libgl-dev
 Architecture: any
 Depends:
  libgl1 (= ${binary:Version}),
+ libglx-dev,
  ${misc:Depends},
 Replaces:
  libgl1-mesa-dev (<< 19.3.0~rc6-1),