/O2 needs set

[DaMan]

With the change to VS08 bzip2, fixrtext, game-music-emu, jpeg-6b, lmzalib x64, update rev, zipdir, and zlib are affected by this bug.
The change also breaks Win9x support so a footnote on the current version stating last version to support Win9x might be helpful to someone.

[Graf Zahl]

The VS project files have been effectively deprecated, just waiting for a decision by ZDoom to delete them entirely - and they will no longer be maintained. I just cannot delete them without causing problems with ZDoom updates.

Please use CMake to create working projects from now on.