fix initial build from git

we need to ignore the absence of VERSION, as aclocal executes the
include() while ignoring the prior m4_syscmd().

configure.ac

@@ -3,7 +3,7 @@
 dnl SPDX-License-Identifier: GPL-2.0-or-later
 
 m4_syscmd([./version.sh])
-AC_INIT([isync], m4_include([VERSION]))
+AC_INIT([isync], m4_sinclude([VERSION]))
 AC_CONFIG_HEADERS([autodefs.h])
 
 AC_CANONICAL_TARGET