libcacard: actually use symbols file

libcacard: actually use symbols file

libtool has an argument for .syms file, which is -export-symbols.
There's no argument `-export-syms', and it looks like at least on
linux, -export-syms is just ignored.  Use the correct argument,
-export-symbols, to actually get the right export list.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Alon Levy <alevy@redhat.com>
Tested-by: Alon Levy <alevy@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>