meson: use config_base_arch for target libraries

meson: use config_base_arch for target libraries

Fixed commit introduced common dependencies for target libraries. Alas,
it wrongly reused the 'target' variable, which was previously set from
another loop.

Thus, some dependencies were missing depending on order of target list,
as found here [1].

The fix is to use the correct config_base_arch instead.
Kudos to Thomas Huth who had this right, before I reimplement it, and
introduce this bug.

[1] https://lore.kernel.org/qemu-devel/c54469ce-0385-4aea-b345-47711e9e61de@linaro.org/

Fixes: 4fb54de823e9 (meson: build target libraries with common dependencies)
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Tested-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/r/20250602233801.2699961-1-pierrick.bouvier@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>