clover: empty soversion when on win32
Closes: mesa/mesa#7675 Cc: mesa-stable Signed-off-by:Yonggang Luo <luoyonggang@gmail.com> Reviewed-by:
Prodea Alexandru-Liviu <liviuprodea@yahoo.com> Part-of: <mesa/mesa!19653> (cherry picked from commit 14eef141)