[llvm-rc] Serialize MENU resources to .res files (serialization, pt 3).

This allows MENU resources to be serialized.

MENU resource statement doc:
msdn.microsoft.com/en-us/library/windows/desktop/aa381025.aspx
POPUP sub-statement doc:
msdn.microsoft.com/en-us/library/windows/desktop/aa381030.aspx
MENUITEM sub-statement doc:
msdn.microsoft.com/en-us/library/windows/desktop/aa381024.aspx
MENUHEADER structure:
msdn.microsoft.com/en-us/library/windows/desktop/ms648018.aspx (and
NORMALMENUITEM, POPUPMENUITEM structs).

Thanks for Nico Weber for his original work in this area.

Differential Revision: https://reviews.llvm.org/D37828

llvm-svn: 314562