Work around crash in wxStyledTextCtrl under Mac

When not using double buffering, double-clicking to select text in the
control results in crashes.

Avoid this by using double-buffering under Mac, even though it shouldn't
be necessary.

This reverts the changes of cb79948
under Mac.

See wxWidgets#18085.

src/stc/stc.cpp

@@ -224,8 +224,9 @@ bool wxStyledTextCtrl::Create(wxWindow *parent,
     // STC doesn't support RTL languages at all
     SetLayoutDirection(wxLayout_LeftToRight);
 
-    // Rely on native double buffering by default.
-#if wxALWAYS_NATIVE_DOUBLE_BUFFER
+    // Rely on native double buffering by default, except under Mac where it
+    // doesn't work for some reason, see #18085.
+#if wxALWAYS_NATIVE_DOUBLE_BUFFER && !defined(__WXMAC__)
     SetBufferedDraw(false);
 #else
     SetBufferedDraw(true);