Currently VSS dll/tlb files for use in w32 builds are only built as a
result of having been added to the general 'tools' target alongside
qemu-ga. This is fine for default make target, but if we build
qemu-ga directly via `make qemu-ga.exe`, the VSS files are not
created.

Fix this by moving the VSS dependencies to qemu-ga.exe directly.
With this move we can move the VSS files back out of 'tools',
and drop the extra handling from MSI target in Makefile.

Now we can build qemu-ga MSI package with:
  ./configure ...
  make qemu-ga.exe
  make msi

or simply:
  ./configure ...
  make msi

and no longer need to do a full build beforehand.
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>