patch 9.0.1964: xattr support fails to build on MacOS X

Problem:  xattr support fails to build on MacOS X
Solution: Disable xattr support for MacOS X

MacOS X uses the same headers and functions sys/xattr.h but the function
signatures for xattr support are much different, so building fails.

So let's for now disable xattr support there.

closes: #13230
closes: #13232

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/feature.h b/src/feature.h
index b26dc6c..5fcd727 100644
--- a/src/feature.h
+++ b/src/feature.h
@@ -1177,9 +1177,9 @@
 #endif
 
 /*
- * XATTR support
+ * currently Unix only: XATTR support
  */
 
-#if defined(FEAT_NORMAL) && defined(HAVE_XATTR)
+#if defined(FEAT_NORMAL) && defined(HAVE_XATTR) && !defined(MACOS_X)
 # define FEAT_XATTR
 #endif