brltty: fix cross with Python 3.8.

srcpkgs/brltty/template

@@ -1,7 +1,7 @@
 # Template file for 'brltty'
 pkgname=brltty
 version=6.0
-revision=3
+revision=4
 build_style=gnu-configure
 configure_args="--enable-gpm --with-screen-driver=lx,sc
  --with-tables-directory=/usr/share/brltty PYTHON=/usr/bin/python3"
@@ -38,6 +38,20 @@ post_configure() {
 	esac
 }
 
+pre_build() {
+	if [ "$CROSS_BUILD" ]; then
+		for f in ${XBPS_CROSS_BASE}/${py3_lib}/_sysconfigdata_*; do
+			f=${f##*/}
+			export _PYTHON_SYSCONFIGDATA_NAME=${f%.py}
+		done
+		export PYTHONPATH=${XBPS_CROSS_BASE}/${py3_lib}
+	fi
+}
+
+pre_install() {
+	pre_build
+}
+
 do_install() {
 	make INSTALL_ROOT=${DESTDIR} install
 	vsv $pkgname