[llvm-rc] Add user-defined resources parsing ability. [8/8]

This allows llvm-rc to parse user-defined resources (ref:
msdn.microsoft.com/en-us/library/windows/desktop/aa381054.aspx).
These statements either import files, or put the specified raw data in
the resulting resource file.

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

Differential Revision: https://reviews.llvm.org/D37033

llvm-svn: 314478