add crcXXgen.c.tpl to EXTRA_DIST

'make distcheck' distributes the generated .c files, but it is good GPL
practice to also distribute the template.

Change-Id: I988acd3bc629e98985a99780d3142112125d13f7
diff --git a/Makefile.am b/Makefile.am
index 7390f98..d08f41b 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -68,6 +68,7 @@
 $(top_builddir)/doc/libosmocore.tag.prep: $(top_builddir)/Doxyfile.core \
 		$(top_srcdir)/include/osmocom/core/*.h \
 		$(top_srcdir)/src/*.[hc] \
+		$(top_srcdir)/src/crcXXgen.c.tpl \
 		$(top_srcdir)/src/pseudotalloc/*.[hc]
 	rm -rf $(top_builddir)/doc/core; mkdir -p $(top_builddir)/doc/core
 	rm -rf $(top_builddir)/doc/libosmocore.map