Fix entry point in Unicode build of the MFC sample.

Fix entry point in Unicode build of the MFC sample.

MFC needs the entry point to be wWinMainCRTStartup() in Unicode builds but the
bakefile-generated projects use the default WinMain() so the sample didn't
link in Unicode.

Fix this by providing WinMain() which simply forwards to wWinMainCRTStartup()
as this seems to work for all MSVC/CRT versions.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66667 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775