temporarily set the FRAG_BIT_FOGC bit in InputsRead when fog is enabled

(cherry picked from commit 63be96bdc7)

src/mesa/main/texenvprogram.c

@@ -1100,6 +1100,7 @@ create_new_program(GLcontext *ctx, struct state_key *key,
        * a reduced value and not what is expected in FogOption
        */
       p.program->FogOption = ctx->Fog.Mode;
+      p.program->Base.InputsRead |= FRAG_BIT_FOGC; /* XXX new */
    } else
       p.program->FogOption = GL_NONE;