gpg4win: Set product-specific built-in Kleopatra version

Previously, we used "Gpg4win-VERSION" as built-in Kleopatra version for
all products. Usually this doesn't matter because the version is
overwritten by the data read from the signed VERSION file, but it might
matter for the output of --version. I couldn't provoke a wrong version
for a GPD build with signed VERSION file, but it's still a race between
two threads. Long story short, now the correct Kleopatra version is set
at build time.

• GnuPG-bug-id: T7509