mesa: Report ARB_debug_output for both shader errors and warnings.

This ends up reusing the dynamic ID support, so a silly enum gets to go
away.  We don't assign good IDs to different messages yet, but at least
that's tractable now.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/glsl/standalone_scaffolding.h

@@ -44,7 +44,7 @@ extern "C" struct gl_shader *
 _mesa_new_shader(struct gl_context *ctx, GLuint name, GLenum type);
 
 extern "C" void
-_mesa_shader_debug(struct gl_context *ctx, GLenum type, GLuint id,
+_mesa_shader_debug(struct gl_context *ctx, GLenum type, GLuint *id,
                    const char *msg, int len);
 
 /**