* Remove the "version suffix" and BUILD_INFO.txt mechanisms, which I
believe no one uses except winpty itself. Instead, a suffix can be
added in the VERSION.txt file.
* Instead of passing the version and commit info as a preprocessor macro
when building every C++ file, write the info into a GenVersion.h
header that is only included by WinptyVersion.cc.
* Instead of writing a BUILD_INFO.txt in ship.py, pass COMMIT_HASH=<hash>
to make.
These changes accomplish two things:
* People who build a tag from source won't see a "<ver>-dev" suffix
anymore.
* Changing the version or the commit will correctly rebuild the version
object files (and only those object files). It will also relink every
binary.
Fixes https://github.com/rprichard/winpty/issues/72
