glx/tests: Add GetGLXScreenConfigs_called flag

Tests for the GLX_MESA_query_context extension will use this flag.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>

src/glx/tests/create_context_unittest.cpp

@@ -54,11 +54,15 @@ glx_context_init(struct glx_context *gc,
    return GL_TRUE;
 }
 
+bool GetGLXScreenConfigs_called = false;
+
 extern "C" struct glx_screen *
 GetGLXScreenConfigs(Display * dpy, int scrn)
 {
    (void) dpy;
    (void) scrn;
+
+   GetGLXScreenConfigs_called = true;
    return psc;
 }