intel/anv: Use #defines for all __gen_ helpers
intel/anv: Use #defines for all __gen_ helpers

This allows us to #undef them later if we don't want them to persist

Signed-off-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>
Reviewed-by: Topi Pohjolainen <749697f19798b7f640b17221fd283b903825f071@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler