util: _debug_printf should print even when DEBUG is not defined
util: _debug_printf should print even when DEBUG is not defined

The leading underscore is meaningful...  This function is used by
_warning and _error functions as well as the more common
debug_printf().

debug_printf (without underscore) gets turned off when DEBUG is
disabled, but warning/error messages still use this function to get
their message out.
(cherry picked from commit 0ac879dca797360570543d5bd0fd64f8fb8e566e)

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