version script support misdetected when using mold linker

When using mold as a linker libslirp decides it does not support --version-script even though it does. The reason being test for support uses real libslirp.map: https://gitlab.freedesktop.org/slirp/libslirp/-/blob/ce314e39458223c2c42245fe536fbe1bcd94e9b1/meson.build#L144-149

and mold fails if it cannot find symbol that is present in version script:

mold: error: /home/users/builder/rpm/BUILD/libslirp-4.8.0/src/libslirp.map: cannot assign versi
on `SLIRP_4.0` to symbol `slirp_add_exec`: symbol not found
mold: error: /home/users/builder/rpm/BUILD/libslirp-4.8.0/src/libslirp.map: cannot assign version `SLIRP_4.0` to symbol `slirp_add_guestfwd`: symbol not found
mold: error: /home/users/builder/rpm/BUILD/libslirp-4.8.0/src/libslirp.map: cannot assign version `SLIRP_4.0` to symbol `slirp_add_hostfwd`: symbol not found
...