configure: lupdate is not needed for Qt build

Don't require lupdate to build with Qt. Like xgettext it is only
needed to update translations, not for normal builds.

This fixes the gitian build (broken by fcfbf547d).

configure.ac

@@ -165,9 +165,9 @@ BITCOIN_QT_PATH_PROGS([MOC], [moc-qt4 moc4 moc],, $qt_bin_path:$PATH)
 BITCOIN_QT_PATH_PROGS([UIC], [uic-qt4 uic4 uic],, $qt_bin_path:$PATH)
 BITCOIN_QT_PATH_PROGS([RCC], [rcc-qt4 rcc4 rcc],, $qt_bin_path:$PATH)
 BITCOIN_QT_PATH_PROGS([LRELEASE], [lrelease-qt4 lrelease4 lrelease],, $qt_bin_path:$PATH)
-BITCOIN_QT_PATH_PROGS([LUPDATE], [lupdate-qt4 lupdate4 lupdate],, $qt_bin_path:$PATH)
 BITCOIN_QT_PATH_PROGS([PROTOC], [protoc],, $protoc_bin_path:$PATH)
 AC_PATH_PROG(CCACHE,ccache)
+AC_PATH_PROGS([LUPDATE], [lupdate-qt4 lupdate4 lupdate],, $qt_bin_path:$PATH)
 AC_PATH_PROG(XGETTEXT,xgettext)
 AC_PATH_PROG(HEXDUMP,hexdump)
 PKG_PROG_PKG_CONFIG