Just as an extra data point, this issue and the workaround from comment #5 seem
to apply also to X-Plane 11. Tested with a Radeon RX 560 on Fedora 27 with the
stock drivers. Currently this would be:

kernel 4.13.12-300
mesa 17.2.4-2

With the MESA_EXTENSION_OVERRIDE=-GL_AMD_pinned_memory ./X-Plane-x86_64
workaround, the simulator works ok.