Fix parallel make (again) - the phony target trick doesn't work

This partly reverts c7087ebce9f035d436a9b215657a91e5a8463aed

I am aware that creating dependencies on vcc_if.h doesn't look as nice
as having a vcc target, but parallel builds just don't work otherwise

src/Makefile.am

@@ -20,10 +20,11 @@ dist_man_MANS = vmod_vtstor.3
 vmod_vtstor.3: vmod_vtstor.man.rst
 	${RST2MAN} $< $@
 
+vmod_vtstor.lo: vcc_if.c
 
-vmod_vtstor.lo vmod_vtstor.man.rst: vcc
+vmod_vtstor.man.rst vcc_if.c: vcc_if.h
 
-vcc: @VMODTOOL@ $(top_srcdir)/src/vmod_vtstor.vcc
+vcc_if.h: @VMODTOOL@ $(top_srcdir)/src/vmod_vtstor.vcc
 	@PYTHON@ @VMODTOOL@ $(top_srcdir)/src/vmod_vtstor.vcc
 
 VTC_LOG_COMPILER = $(VARNISHTEST) -v \
@@ -31,7 +32,7 @@ VTC_LOG_COMPILER = $(VARNISHTEST) -v \
 TEST_EXTENSIONS = .vtc
 TESTS = @VMOD_TESTS@
 
-@VMOD_TESTS@: vcc
+@VMOD_TESTS@: vmod_vtstor.lo
 
 EXTRA_DIST = \
 	vmod_vtstor.vcc \