Add XMLWRAPP_DEPRECATED message support for GCC and VC++.

GCC supports deprecation messages since 4.5 and Visual C++ since 2005,
so use it.  Also fix incorrect Visual C++ checks so that it actually
works now.

Reference:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43666
http://msdn.microsoft.com/en-us/library/044swk7y(v=vs.80).aspx