Set SYSCONFDIR to /etc/xdg by default, otherwise the default and current
value is /usr/local/etc/xdg which does not exist.

OK? Feedback?

diff --git a/x11/qt6/qtbase/Makefile b/x11/qt6/qtbase/Makefile
index 9bf9420cb0a..26856fb9086 100644
--- a/x11/qt6/qtbase/Makefile
+++ b/x11/qt6/qtbase/Makefile
@@ -4,6 +4,7 @@ COMMENT-main =		C++ general-purpose toolkit
 COMMENT-global =	global Qt6 documentation internals
 COMMENT-mysql =		MySQL plugin for Qt6
 COMMENT-psql =		PostgresSQL plugin for Qt6
+REVISION-main =		0
 
 PKGSPEC-main =		qt6-qtbase-${QT6_PKGSPEC}
 
@@ -127,7 +128,8 @@ CONFIGURE_ARGS +=	-DBUILD_WITH_PCH=OFF \
 			-DINSTALL_EXAMPLESDIR=share/doc/qt6/examples \
 			-DINSTALL_INCLUDEDIR=include/X11/qt6 \
 			-DINSTALL_MKSPECSDIR=lib/qt6/mkspecs \
-			-DINSTALL_PLUGINSDIR=lib/qt6/plugins
+			-DINSTALL_PLUGINSDIR=lib/qt6/plugins \
+			-DINSTALL_SYSCONFDIR=${SYSCONFDIR}/xdg
 
 # TODO
 #CONFIGURE_ARGS +=	-DQT_BUILD_TESTS=ON