lint fixes:
1. avoid typedef re-definitions (perhaps introduce c11 mode for lint)
2. add __lint__ wherever __GNUC__ is defined.

avoid xnack, and -fp32-denormals, and +fp64-denormals options for
amdgpu / radeonsi driver. these options don't work with llvm 13,
and generate warnings for all GL apps.

mesa 21 has entirely different code here.

initial import of Mesa 19.1.7 into MesaLib.old.