build: Let configure create the VERSION file.

* autogen.sh: Update from libgpg-error.
* configure.ac: Use mym4_* things to create VERSION file.
* Makefile.am (dist-hook): Do not create VERSION.
(EXTRA_DIST): Add VERSION.

Now, configure displays

npth v1.6 prepared for make

instead of "npth-1.6".

• GnuPG-bug-id: T3283
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>