vc4: Add better debug of NIR->QIR control flow graph failure
vc4: Add better debug of NIR->QIR control flow graph failure

Ensure NIR control flow graph nodes that are unhandled in QIR
are reported with sufficient verbosity to aid debugging.

This improves piglit outputs, amongst other tools.

There are no other remaining uses of assert(0) as a blunt tool
within vc4.

Signed-off-by: Rhys Kidd <0b3b315d08353e2046d43a86d41e3fd1dff3d6ad@gmail.com>
Reviewed-by: Eric Anholt <96f164ad4d9b2b0dacf8ebee2bb1eeb3aa69adf1@anholt.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler