add marcos to fix build

Signed-off-by: Luke Yue <lukedyue@gmail.com>

xfce4-panel.spec

@@ -5,7 +5,7 @@
 
 Name:           xfce4-panel
 Version:        4.14.4
-Release:        1%{?dist}
+Release:        2
 Summary:        panel for Xfce4 desktop environment
 License:        GPLv2+ and LGPLv2+
 #Group:          Development/Libraries
@@ -60,7 +60,12 @@ plugins for xfce4-panel.
 sed -i 's|Icon=office-calendar|Icon=xfce4-clock|g' plugins/clock/clock.desktop.in.in
 
 %build
-%configure --enable-gtk-doc --disable-static 
+%configure \
+%if !%{_with_vala}
+ --enable-vala=no \
+%endif
+ --enable-gtk-doc \
+ --disable-static 
 
 # Remove rpaths
 sed -i 's|^hardcode_libdir_flag_spec=.*|hardcode_libdir_flag_spec=""|g' libtool