Here's a pair of patches, the first patching all non-absolute dlopen()
uses I could detect (except for GBM), and the second enabling a few
optional features of Mesa, including GBM, and adding that last GBM
dlopen() patch.  (My intent is to keep the patches stylistically
agnostic to each other; I guess it doesn't really matter much.)  (And
FWIW, GBM is enabled automatically when one enables the DRM platform
support for EGL...)