Define wxNOEXCEPT similarly to the existing wxOVERRIDE

Also define wxHAS_NOEXCEPT allowing to check if noexcept is supported.

This is not used in the library yet, but probably should be.

docs/doxygen/mainpages/const_cpp.h

@@ -188,6 +188,7 @@ Currently the following symbols exist:
 @itemdef{wxHAS_NATIVE_ANIMATIONCTRL, Defined if native wxAnimationCtrl class is being used (this symbol only exists in wxWidgets 3.1.4 and later).}
 @itemdef{wxHAS_NATIVE_DATAVIEWCTRL, Defined if native wxDataViewCtrl class is being used (this symbol only exists in wxWidgets 3.1.4 and later).}
 @itemdef{wxHAS_NATIVE_WINDOW, Defined if wxNativeWindow class is available.}
+@itemdef{wxHAS_NOEXCEPT, Defined if the currently used compiler supports C++11 @c noexcept. @c wxNOEXCEPT is defined as this keyword in this case, and as nothing otherwise.}
 @itemdef{wxHAS_NULLPTR_T, Defined if the currently used compiler supports C++11 @c nullptr.}
 @itemdef{wxHAS_IMAGES_IN_RESOURCES, Defined if <a href="http://en.wikipedia.org/wiki/Resource_(Windows)">
     Windows resource files</a> or OS/2 resource files are available on the current platform.}

include/wx/defs.h

@@ -285,6 +285,14 @@ typedef short int WXTYPE;
     #define wxOVERRIDE
 #endif /*  HAVE_OVERRIDE */
 
+/* same for noexcept keyword */
+#if __cplusplus >= 201703L || wxCHECK_VISUALC_VERSION(14)
+    #define wxHAS_NOEXCEPT
+    #define wxNOEXCEPT noexcept
+#else
+    #define wxNOEXCEPT
+#endif
+
 /*
     Support for nullptr is available since MSVS 2010, even though it doesn't
     define __cplusplus as a C++11 compiler.