This adds a configure knob to Qt itself, which responds to the
FreeBSD Makefile knobs; otherwise, we can't turn off finding
OpenAL when it is installed.

--- src/multimedia/configure.json.orig	2020-10-27 08:02:12 UTC
+++ src/multimedia/configure.json
@@ -13,6 +13,7 @@
             "directshow": { "type": "boolean" },
             "wmf": { "type": "boolean" },
             "gstreamer": { "type": "optionalString", "values": [ "no", "yes", "0.10", "1.0" ] },
+            "openal": "boolean",
             "pulseaudio": "boolean"
         }
     },
@@ -101,9 +102,9 @@
         "gstreamer_gl_1_0": {
             "label": "GStreamer OpenGL 1.0",
             "export": "gstreamer_gl",
             "test":  {
-                "include": "gst/gl/gl.h"
+                "include": "gst/gl/gl.h-BogusNotFound"
             },
             "use": "gstreamer_1_0",
             "sources": [
                 { "type": "pkgConfig", "args": "gstreamer-gl-1.0" }