Allow external settings of MAX_WIDTH/HEIGHT.
Allow external settings of MAX_WIDTH/HEIGHT.

Conditionalize MAX_WIDTH / MAX_HEIGHT defines so that users can
set them via CFLAGS.

(cherry picked from master, commit 66bc17e80e22d8f205cc02171b1c266feab6631f)

metora/MesaGLSLCompiler,wolf96/glsl-optimizer,zeux/glsl-optimizer,mapbox/glsl-optimizer,zz85/glsl-optimizer,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,mapbox/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,KTXSoftware/glsl2agal,djreep81/glsl-optimizer,mapbox/glsl-optimizer,zeux/glsl-optimizer,benaadams/glsl-optimizer,zz85/glsl-optimizer,mapbox/glsl-optimizer,jbarczak/glsl-optimizer,wolf96/glsl-optimizer,benaadams/glsl-optimizer,jbarczak/glsl-optimizer,KTXSoftware/glsl2agal,benaadams/glsl-optimizer,benaadams/glsl-optimizer,mcanthony/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,zz85/glsl-optimizer,metora/MesaGLSLCompiler,mapbox/glsl-optimizer,zeux/glsl-optimizer,adobe/glsl2agal,djreep81/glsl-optimizer,tokyovigilante/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,jbarczak/glsl-optimizer,metora/MesaGLSLCompiler,zeux/glsl-optimizer,KTXSoftware/glsl2agal,dellis1972/glsl-optimizer,adobe/glsl2agal,mcanthony/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,bkaradzic/glsl-optimizer,wolf96/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,KTXSoftware/glsl2agal,bkaradzic/glsl-optimizer,KTXSoftware/glsl2agal,jbarczak/glsl-optimizer,adobe/glsl2agal,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,tokyovigilante/glsl-optimizer,djreep81/glsl-optimizer,adobe/glsl2agal,dellis1972/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,adobe/glsl2agal,dellis1972/glsl-optimizer,zz85/glsl-optimizer