Feed automake a pkgdatadir

While at it, get rid of the hard-coded package name.

Refs #2251

bin/varnishd/Makefile.am

@@ -140,13 +140,15 @@ nobase_pkginclude_HEADERS = \
 	common/com_params.h \
 	waiter/waiter.h
 
+pkgdatadir = ${datarootdir}/${PACKAGE}/vcl
+
 varnishd_CFLAGS = \
 	@PCRE_CFLAGS@ \
 	@SAN_CFLAGS@ \
 	-DVARNISHD_IS_NOT_A_VMOD \
 	-DVARNISH_STATE_DIR='"${VARNISH_STATE_DIR}"' \
 	-DVARNISH_VMOD_DIR='"${pkglibdir}/vmods"' \
-	-DVARNISH_VCL_DIR='"${varnishconfdir}:${datarootdir}/varnish/vcl"'
+	-DVARNISH_VCL_DIR='"${varnishconfdir}:${pkgdatadir}"'
 
 varnishd_LDFLAGS = -export-dynamic