Gitignore MacOS files.

* This copies a patch for YAXT by Sergey Kosukhin.

.gitignore

@@ -96,6 +96,10 @@ Makefile
 /test/testsuite.dir
 /test/testsuite.log
 
+# On MacOS debug builds may produce these files/directories:
+*.dSYM
+.DS_Store
+
 # Dist stage files:
 /ppm-*.tar*