* OpenGL 4.5 support for RadeonSI and recent Intel
* Use LLVM 4.0 by default, building with 3.9 is possible via MESA_LLVM_VER
* DRI3 remains enabled at compile time, but is now disabled at runtime for
stock FreeBSD. Set LIBGL_DRI3_ENABLE in the environment to enable DRI3.
This extra check is added when compiling on stock FreeBSD, not DRM-next.
This change was made to work around a problem in libEGL, which fails to
fall back to using DRI2 when run on a system without DRI3 support.
Reviewed by: jmd, mat
Approved by: swills (mentor)
Differential Revision: https://reviews.freebsd.org/D10250
ef2181dc7a