build: do not build/link harfbuzz on macOS

src/font/face/coretext.zig

@@ -28,7 +28,7 @@ pub const Face = struct {
 
     /// True if our build is using Harfbuzz. If we're not, we can avoid
     /// some Harfbuzz-specific code paths.
-    const harfbuzz_shaper = font.Shaper == font.shape.harfbuzz.Shaper;
+    const harfbuzz_shaper = font.options.backend.hasHarfbuzz();
 
     /// The matrix applied to a regular font to auto-italicize it.
     pub const italic_skew = macos.graphics.AffineTransform{

src/font/main.zig

@@ -115,6 +115,19 @@ pub const Backend = enum {
             => false,
         };
     }
+
+    pub fn hasHarfbuzz(self: Backend) bool {
+        return switch (self) {
+            .freetype,
+            .fontconfig_freetype,
+            .coretext_freetype,
+            => true,
+
+            .coretext,
+            .web_canvas,
+            => false,
+        };
+    }
 };
 
 /// The styles that a family can take.

src/main_ghostty.zig

@@ -256,7 +256,9 @@ pub const GlobalState = struct {
         std.log.info("ghostty build optimize={s}", .{build_config.mode_string});
         std.log.info("runtime={}", .{build_config.app_runtime});
         std.log.info("font_backend={}", .{build_config.font_backend});
-        std.log.info("dependency harfbuzz={s}", .{harfbuzz.versionString()});
+        if (comptime build_config.font_backend.hasHarfbuzz()) {
+            std.log.info("dependency harfbuzz={s}", .{harfbuzz.versionString()});
+        }
         if (comptime build_config.font_backend.hasFontconfig()) {
             std.log.info("dependency fontconfig={d}", .{fontconfig.version()});
         }