Looks like this behaviour was introduced with a change to cairo in version 1.12.16-4 [1]. So looks like gtk was depending on being linked to libGL.so indirectly via cairo.
So, any of the below should fix it: 1) Re-enable GL/EGL support in cairo. 2) Add libgl1-mesa-glx as a dependency of gtk. 3) [upstream] Introduce runtime checks before calling GL functions. [1] https://anonscm.debian.org/cgit/collab-maint/cairo.git/commit/?id=a4bad9f8463d3e1ed2ebe15890c5c52c1c29a271
