swrast: Enable GL_EXT_separate_shader_objects in software paths

src/mesa/main/extensions.c

@@ -261,6 +261,7 @@ _mesa_enable_sw_extensions(struct gl_context *ctx)
    ctx->Extensions.ARB_point_sprite = GL_TRUE;
 #if FEATURE_ARB_shader_objects
    ctx->Extensions.ARB_shader_objects = GL_TRUE;
+   ctx->Extensions.EXT_separate_shader_objects = GL_TRUE;
 #endif
 #if FEATURE_ARB_shading_language_100
    ctx->Extensions.ARB_shading_language_100 = GL_TRUE;