[llvm-cvtres] Reduce the set of dependencies of llvm-cvtres. NFC.

Don't use createBinary() but call the WindowsResource class directly.
The createBinary() function references all supported object file
types and ends up pulling way more from all the underlying libraries
than what is necessary.

This shrinks a stripped llvm-cvtres from 4.6 MB to 463 KB.

Differential Revision: https://reviews.llvm.org/D100833