gallivm: fix incorrect floor(), itrunc()
gallivm: fix incorrect floor(), itrunc()

LLVMBuildFPTrunc() should be used for double->float conversion, not
float->int conversion.

There should be a better way to compute floor(), ceil(), etc that doesn't
involve float->int->float conversion.

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