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	2019-10-15 04:21:48 UTC
+++ src/multimedia/configure.json
@@ -12,6 +12,7 @@
             "directshow": { "type": "boolean" },
             "wmf": { "type": "boolean" },
             "gstreamer": { "type": "optionalString", "values": [ "no", "yes", "0.10", "1.0" ] },
+            "openal": "boolean",
             "pulseaudio": "boolean"
         }
     },