skalibs: fix cross
skalibs-2.14.0.0 added detection for some weird bug exhibited in
"old glibcs and some virtual platforms". When cross compiling the
detector cannot be run:
> posixspawnearlyreturn: `yes` if the target has a broken
> `posix_spawn()` implementation that can return before the
> child has successfully exec'ed. That happens with old glibcs
> and some virtual platforms.
I just took a wild guess here and picked `no`.
Co-authored-by: Alyssa Ross <hi@alyssa.is>