Allow predefining wxHAS_MODE_T to avoid mode_t conflicts

This symbol can now be predefined to avoid conflicts with mode_t definition in
wx/filefn.h when wxWidgets is used in applications also using another library
which also defines mode_t.

Closes https://github.com/wxWidgets/wxWidgets/pull/165

docs/doxygen/mainpages/const_cpp.h

@@ -199,6 +199,13 @@ Currently the following symbols exist:
 @itemdef{wxHAS_RAW_KEY_CODES, Defined if raw key codes (see wxKeyEvent::GetRawKeyCode are supported.}
 @itemdef{wxHAS_REGEX_ADVANCED, Defined if advanced syntax is available in wxRegEx.}
 @itemdef{wxHAS_TASK_BAR_ICON, Defined if wxTaskBarIcon is available on the current platform.}
+@itemdef{wxHAS_MODE_T, Defined when wxWidgets defines @c mode_t typedef for the
+    compilers not providing it. If another library used in a wxWidgets
+    application, such as ACE (http://www.cs.wustl.edu/~schmidt/ACE.html), also
+    defines @c mode_t, this symbol can be predefined after including the other
+    library header, such as @c "ace/os_include/sys/os_types.h" in ACE case,
+    but before including any wxWidgets headers, to prevent a definition
+    conflict.}
 @endDefList
 
 

include/wx/filefn.h

@@ -44,7 +44,10 @@
 // constants
 // ----------------------------------------------------------------------------
 
-#if defined(__VISUALC__)
+// MSVC doesn't define mode_t, so do it ourselves unless someone else
+// had already predefined it.
+#if defined(__VISUALC__) && !defined(wxHAS_MODE_T)
+    #define wxHAS_MODE_T
     typedef int mode_t;
 #endif