Fix an issue where the order of symbol definition determined if

code could compile or not.

Fixes #1569

bin/varnishtest/tests/r01569.vtc

+varnishtest "symbol lookup order issue"
+
+varnish v1 -vcl {
+	vcl 4.0;
+	import ${vmod_debug};
+
+	backend debug {
+		.host = "127.0.0.1";
+		.port = "80";
+	}
+
+	sub debug {
+		set req.backend_hint = debug;
+	}
+
+	sub vcl_recv {
+		call debug;
+	}
+}

lib/libvcc/vcc_expr.c

@@ -688,7 +688,15 @@ vcc_expr4(struct vcc *tl, struct expr **e, enum var_type fmt)
 		 * XXX: what if var and func/proc had same name ?
 		 * XXX: look for SYM_VAR first for consistency ?
 		 */
-		sym = VCC_FindSymbol(tl, tl->t, SYM_NONE);
+		sym = NULL;
+		if (fmt == BACKEND)
+			sym = VCC_FindSymbol(tl, tl->t, SYM_BACKEND);
+		if (sym == NULL)
+			sym = VCC_FindSymbol(tl, tl->t, SYM_VAR);
+		if (sym == NULL)
+			sym = VCC_FindSymbol(tl, tl->t, SYM_FUNC);
+		if (sym == NULL)
+			sym = VCC_FindSymbol(tl, tl->t, SYM_NONE);
 		if (sym == NULL || sym->eval == NULL) {
 			VSB_printf(tl->sb, "Symbol not found: ");
 			vcc_ErrToken(tl, tl->t);

lib/libvcc/vcc_symb.c

@@ -50,7 +50,6 @@ VCC_SymKind(struct vcc *tl, const struct symbol *s)
 	}
 }
 
-
 static struct symbol *
 vcc_AddSymbol(struct vcc *tl, const char *nb, int l, enum symkind kind)
 {