Don't use -fvisibilty=hidden on cygwin
Don't use -fvisibilty=hidden on cygwin

All it's going to do is generate lots and lots and lots of
'warning: visibility attribute not supported in this configuration; ignored'
warnings

Signed-off-by: Jon TURNEY <45846cba2ea093796a8b1c25d70d679d8107179f@dronecode.org.uk>
Reviewed-by: Dan Nicholson <2570c412b7cbb4203ff39baaca2bd49e72848226@gmail.com>

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