While investigating some strange problems with the KMSDRM driver on SDL2 I have been dealing with for months, I tried to build libgbm from sources.
Latest version I could find is this one on Robclark's repo:
But it's outdated, last commits being from 2012.
According to dpkg, the latest version Raspbian can install is 13.0.6-1+rpi2. Isn't there a newer version of the library? Do you know where are it's sources located?