gallivm: faster iround implementation for sse2
gallivm: faster iround implementation for sse2

sse2 supports round to nearest directly (or rather, assuming default nearest
rounding mode in MXCSR). Use intrinsic to use this rather than round (sse41)
or bit manipulation whenever possible.

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