Add wxNOEXCEPT and use it for std::streambuf-derived classes.

This fixes warnings from Intel compiler about overriding function using a
different exception specification than the base one and also incidentally
provides a handy macro that can be useful in other situations.

Closes #14826.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72978 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/defs.h

@@ -1725,6 +1725,22 @@ template <typename T> wxSwap(T& first, T& second);
 */
 void wxVaCopy(va_list argptrDst, va_list argptrSrc);
 
+/**
+    Macro that can be used to indicate that a function doesn't throw any
+    exceptions.
+
+    This macro expands to `noexcept` when using C++11 compiler or `throw()` for
+    older C++ compilers or nothing when used with a C++ compiler too old to
+    support even this.
+
+    Notice that `noexcept` and `throw()` have different semantics in case an
+    exception @e is thrown, so this macro should be used only if you don't rely
+    on the behaviour provided by the latter but not the former.
+
+    @since 2.9.5
+ */
+#define wxNOEXCEPT
+
 //@}