sync Makefile for generate.py

- missing dependencies in each of the both places of invocation
- vrt_obj.h is generated, so it cannot be a dependency at the same time

notice with out-of-tree parallel build

include/Makefile.am

@@ -111,6 +111,7 @@ nobase_noinst_HEADERS = \
 ## keep in sync with lib/libvcc/Makefile.am
 vcl.h: \
 	    $(top_srcdir)/lib/libvcc/generate.py \
+	    $(top_srcdir)/include/vcc_interface.h \
 	    $(top_srcdir)/include/vdef.h \
 	    $(top_srcdir)/include/vrt.h \
 	    $(top_srcdir)/doc/sphinx/reference/vcl_var.rst

lib/libvcc/Makefile.am

@@ -45,7 +45,7 @@ vcc_obj.c: \
 	    $(top_srcdir)/include/vcc_interface.h \
 	    $(top_srcdir)/include/vdef.h \
 	    $(top_srcdir)/include/vrt.h \
-	    $(top_srcdir)/include/vrt_obj.h
+	    $(top_srcdir)/doc/sphinx/reference/vcl_var.rst
 	mkdir -p $(top_builddir)/include/tbl
 	@PYTHON@ $(top_srcdir)/lib/libvcc/generate.py \
 	    $(top_srcdir) $(top_builddir)