[llvm-rc] Serialize STRINGTABLE statements to .res file.
This allows llvm-rc to serialize STRINGTABLE resources.
These are output in an unusual way: we locate them at the end of the
file, and strings are merged into bundles of max 16 strings, depending
on their IDs, language, and characteristics.
Patch by: Marek Sokolowski
Differential Revision: https://reviews.llvm.org/D38420