patch 9.0.0694: no native sound support on Mac OS

Problem:    No native sound support on Mac OS.
Solution:   Add sound support for Mac OS. (Yee Cheng Chin, closes #11274)
diff --git a/src/feature.h b/src/feature.h
index bc259fd..2c65253 100644
--- a/src/feature.h
+++ b/src/feature.h
@@ -484,7 +484,7 @@
 #endif
 
 /*
- * sound - currently only with libcanberra
+ * sound
  */
 #if !defined(FEAT_SOUND) && defined(HAVE_CANBERRA)
 # define FEAT_SOUND