Disable utf8 chars on external harfbuzz

crates/xdv/examples/xdvdump.rs

@@ -154,6 +154,7 @@ fn main() {
         )
         .arg(
             Arg::new("PATH")
+                .value_parser(clap::value_parser!(PathBuf))
                 .help("The path to the XDV or SPX file")
                 .required(true)
                 .index(1),

tests/tex-outputs.rs

@@ -199,6 +199,9 @@ fn file_encoding() {
         .go()
 }
 
+// Works around an issue where old (~2.7) Harfbuzz lays out glyphs differently.
+// Remove this once all external Harfbuzz versions don't exhibit the glyph-swapping behavior.
+#[cfg(not(feature = "external-harfbuzz"))]
 #[test]
 fn utf8_chars() {
     TestCase::new("utf8_chars")