Add name offset flags, for parity with cvtres.exe.

Summary:
The original cvtres.exe sets the high bit when an identifier offset
points to a string.  Even though this is not mentioned in the spec, and
in fact does not seem to cause errors with most cases, for some reason
this causes a failure in Chromium where the new resource file is not
verified as a new version.  This patch sets this high bit flag, and also
adds a test case to check that the output of our library is always
identical to original cvtres.

Reviewers: zturner, ruiu

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D35099

llvm-svn: 307452