[llvm-rc] Serialize user-defined resources to .res files.

This allows rc to serialize user-defined resources, as
documented at:

msdn.microsoft.com/en-us/library/windows/desktop/aa381054.aspx

Escape sequences are yet unavailable, and are to be added in one of
child patches.

Patch by: Marek Sokolowski

Differential Revision: https://reviews.llvm.org/D38423

llvm-svn: 315117