glapi: Do not use backtrace on OpenBSD.
glapi: Do not use backtrace on OpenBSD.

execinfo.h is not available on OpenBSD.

Signed-off-by: Vinson Lee <25a259f709b0f1b620605d2518271a846d8826e5@freedesktop.org>
Reviewed-by: Chad Versace <a557f7f75bf28dc19ac99107f5cc7cd6b3fbdb1a@linux.intel.com>

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