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.

add missed files due to being in subdir called 'core'.
this time into the right place.

initial import of Mesa 19.1.7 into MesaLib.old.