try

sbin/build_deb.sh

@@ -20,6 +20,9 @@ QMAKE_ARGS=()
 if [[ -n "${QMAKESPEC:-}" ]]; then
   QMAKE_ARGS+=("-spec" "$QMAKESPEC")
 fi
+if [[ -n "${QMAKE_QTCONF:-}" ]]; then
+  QMAKE_ARGS+=("-qtconf" "$QMAKE_QTCONF")
+fi
 if [[ -n "${QMAKE_CC:-}" ]]; then
   QMAKE_ARGS+=("QMAKE_CC=$QMAKE_CC")
 fi