Fixes for el6 spec file

Some minor adjustments to sync up the el6 spec file with fedora.
diff --git a/contrib/packages/rpm/el6/SPECS/tigervnc.spec b/contrib/packages/rpm/el6/SPECS/tigervnc.spec
index 3667979..d16a416 100644
--- a/contrib/packages/rpm/el6/SPECS/tigervnc.spec
+++ b/contrib/packages/rpm/el6/SPECS/tigervnc.spec
@@ -27,6 +27,9 @@
 BuildRequires: desktop-file-utils, java-devel, jpackage-utils
 BuildRequires: libjpeg-turbo-devel, gnutls-devel, pam-devel
 BuildRequires: cmake28
+%ifnarch s390 s390x
+BuildRequires: xorg-x11-server-devel
+%endif
 
 BuildRequires: openmotif-devel
 Requires: openmotif, openmotif22
@@ -191,14 +194,14 @@
 autoreconf -fiv
 %configure \
 	--disable-xorg --disable-xnest --disable-xvfb --disable-dmx \
-	--disable-xwin --disable-xephyr --disable-kdrive --with-pic \
-	--disable-static --disable-xinerama \
+	--disable-xwin --disable-xephyr --disable-kdrive --disable-wayland \
+	--with-pic --disable-static --disable-xinerama \
 	--with-default-font-path="catalogue:%{_sysconfdir}/X11/fontpath.d,built-ins" \
-  --with-serverconfig-path=/usr/%{_libdir}/xorg \
+	--with-serverconfig-path=%{_libdir}/xorg \
 	--with-fontrootdir=%{_datadir}/X11/fonts \
 	--with-xkb-output=%{_localstatedir}/lib/xkb \
 	--enable-install-libxf86config \
-	--enable-glx --disable-dri --enable-dri2 \
+	--enable-glx --enable-glx-tls --disable-dri --enable-dri2 --disable-dri3 \
 	--disable-config-dbus \
 	--disable-config-hal \
 	--disable-config-udev \