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
Zachary Turner