st/mesa: disable the shader cache if dumping shaders
st/mesa: disable the shader cache if dumping shaders

otherwise, cached shaders aren't dumped.

Reviewed-by: Timothy Arceri <c48760dafc316d20cf5b0817150c999e82cd892f@itsqueeze.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler