Define wxMEMBER_DEFAULT similarly to the existing wxOVERRIDE

Also define wxHAS_MEMBER_DEFAULT allowing to check if '= default' is supported
(compilers that define c++11 and VS2015 and later).

docs/doxygen/mainpages/const_cpp.h

@@ -171,6 +171,9 @@ Currently the following symbols exist:
     wxBitmapToggleButton class is available in addition to wxToggleButton.}
 @itemdef{wxHAS_CONFIG_TEMPLATE_RW, Defined if the currently used compiler
     supports template Read() and Write() methods in wxConfig.}
+@itemdef{wxHAS_MEMBER_DEFAULT, Defined if the currently used compiler supports
+    C++11 @c =default. @c wxMEMBER_DEFAULT is defined as this keyword in this
+    case, and as nothing otherwise.}
 @itemdef{wxHAS_LARGE_FILES, Defined if wxFile supports files more than 4GB in
     size (notice that you must include @c wx/filefn.h before testing for this
     symbol).}

include/wx/animate.h

@@ -38,9 +38,9 @@ public:
     wxAnimation();
     explicit wxAnimation(const wxString &name, wxAnimationType type = wxANIMATION_TYPE_ANY);
 
-#if __cplusplus >= 201103
-    wxAnimation(const wxAnimation&) = default;
-    wxAnimation& operator=(const wxAnimation&) = default;
+#ifdef wxHAS_MEMBER_DEFAULT
+    wxAnimation(const wxAnimation&) wxMEMBER_DEFAULT;
+    wxAnimation& operator=(const wxAnimation&) wxMEMBER_DEFAULT;
 #endif
 
     bool IsOk() const;

include/wx/defs.h

@@ -285,6 +285,14 @@ typedef short int WXTYPE;
     #define wxOVERRIDE
 #endif /*  HAVE_OVERRIDE */
 
+/* same for defaulted member function keyword */
+#if __cplusplus >= 201103L || wxCHECK_VISUALC_VERSION(14)
+    #define wxHAS_MEMBER_DEFAULT
+    #define wxMEMBER_DEFAULT = default
+#else
+    #define wxMEMBER_DEFAULT
+#endif
+
 /*
     Support for nullptr is available since MSVS 2010, even though it doesn't
     define __cplusplus as a C++11 compiler.

include/wx/unichar.h

@@ -267,8 +267,8 @@ public:
     wxUniCharRef& operator=(const wxUniCharRef& c)
         { if (&c != this) *this = c.UniChar(); return *this; }
 
-#if __cplusplus >= 201103
-    wxUniCharRef(const wxUniCharRef&) = default;
+#ifdef wxHAS_MEMBER_DEFAULT
+    wxUniCharRef(const wxUniCharRef&) wxMEMBER_DEFAULT;
 #endif
 
 #define wxUNICHAR_REF_DEFINE_OPERATOR_EQUAL(type) \