Fail on recursive use of vcl `include`

Fixes:	#3360

bin/varnishtest/tests/r03360.vtc

+varnishtest "Test recusive vcl includes"
+
+shell {echo include '"_recurse.vcl";' > ${tmpdir}/_recurse.vcl}
+shell {echo include '"_recurse2.vcl";' > ${tmpdir}/_recurse1.vcl}
+shell {echo include '"_recurse1.vcl";' > ${tmpdir}/_recurse2.vcl}
+
+varnish v1 -arg "-p vcl_path=${tmpdir}" -errvcl "Recursive include of" {
+	backend b { .host = "127.0.0.1"; }
+	include "_recurse.vcl" ;
+} 
+
+varnish v2 -arg "-p vcl_path=${tmpdir}" -errvcl "Recursive include of" {
+	backend b { .host = "127.0.0.1"; }
+	include "_recurse1.vcl" ;
+} 

lib/libvcc/vcc_compile.c

@@ -553,6 +553,7 @@ vcc_resolve_includes(struct vcc *tl)
 {
 	struct token *t, *t1, *t2;
 	struct source *sp;
+	const struct source *sp1;
 	struct vsb *vsb;
 	const char *p;
 
@@ -607,6 +608,22 @@ vcc_resolve_includes(struct vcc *tl)
 			vcc_ErrWhere(tl, t1);
 			return;
 		}
+
+		for (sp1 = t->src; sp1 != NULL; sp1 = sp1->parent)
+			if (!strcmp(sp1->name, sp->name))
+				break;
+		if (sp1 != NULL) {
+			VSB_printf(tl->sb,
+			    "Recursive include of \"%s\"\n\n", sp->name);
+			vcc_ErrWhere(tl, t1);
+			for (sp1 = t->src; sp1 != NULL; sp1 = sp1->parent) {
+				if (sp1->parent_tok)
+					vcc_ErrWhere(tl, sp1->parent_tok);
+			}
+			return;
+		}
+		sp->parent = t->src;
+		sp->parent_tok = t1;
 		VTAILQ_INSERT_TAIL(&tl->sources, sp, list);
 		sp->idx = tl->nsources++;
 		tl->t = t2;

lib/libvcc/vcc_compile.h

@@ -85,6 +85,8 @@ struct source {
 	const char		*e;
 	unsigned		idx;
 	char			*freeit;
+	const struct source	*parent;
+	const struct token	*parent_tok;
 };
 
 struct token {