Handle src/vmod_vcs_version.txt

Since VC 7.7, vmodtool.py generates a file that
must be taken into account in Makefile.am
https://varnish-cache.org/docs/trunk/whats-new/upgrading-7.7.html

.gitignore

@@ -29,3 +29,5 @@ Makefile.in
 /src/vcc_*_if.c
 /src/vcc_*_if.h
 /src/vmod_*rst
+
+src/vmod_vcs_version.txt

Makefile.am

@@ -2,6 +2,10 @@ ACLOCAL_AMFLAGS = -I m4 -I ${VARNISHAPI_DATAROOTDIR}/aclocal
 
 SUBDIRS = src
 
+EXTRA_DIST = src/vmod_vcs_version.txt
+
+DISTCLEANFILES = src/vmod_vcs_version.txt
+
 README.rst: src/vmod_blobsynth.vcc
 	$(MAKE) $(AM_MAKEFLAGS) -C src vmod_blobsynth.man.rst
 	cp src/vmod_blobsynth.man.rst README.rst