main/extensions: Create extra extensions override string
main/extensions: Create extra extensions override string

This will allow us to utilize the early MESA_EXTENSION_OVERRIDE
parsing at the later extension string initialization step.

Signed-off-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
Reviewed-by: Anuj Phogat <e2026475996c48f0b97fd37e84129b3912980428@gmail.com>

bkaradzic/glsl-optimizer,bkaradzic/glsl-optimizer,mcanthony/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,zeux/glsl-optimizer,wolf96/glsl-optimizer,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,djreep81/glsl-optimizer,wolf96/glsl-optimizer,djreep81/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,metora/MesaGLSLCompiler,zz85/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,jbarczak/glsl-optimizer,jbarczak/glsl-optimizer,benaadams/glsl-optimizer,zz85/glsl-optimizer,zz85/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,zz85/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,benaadams/glsl-optimizer,zeux/glsl-optimizer,dellis1972/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,zeux/glsl-optimizer,benaadams/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,metora/MesaGLSLCompiler,djreep81/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,bkaradzic/glsl-optimizer,metora/MesaGLSLCompiler,dellis1972/glsl-optimizer