Support paths for vintf_fragments from Soong.

The property vintf_fragments accepts paths and references to other
modules; however, none of that is passed onto make, resulting in errors
if a non-local path is used.

Test: m
Bug: 184567830
Change-Id: If3b56ea8eec3b95b3a310b58bffd045cedd8ee52

apex/apex_test.go

@@ -2755,7 +2755,7 @@ func TestAndroidMkWritesCommonProperties(t *testing.T) {
 	var builder strings.Builder
 	data.Custom(&builder, name, prefix, "", data)
 	androidMk := builder.String()
-	ensureContains(t, androidMk, "LOCAL_VINTF_FRAGMENTS := fragment.xml\n")
+	ensureContains(t, androidMk, "LOCAL_FULL_VINTF_FRAGMENTS := fragment.xml\n")
 	ensureContains(t, androidMk, "LOCAL_FULL_INIT_RC := init.rc\n")
 }