in reply to rand and srand across builds and platforms?

It will not. See the various Japhs floating around that (a)buse (s)rand to produce an appropriate string. They aren't cross-platform. For instance, from t/japh/abigail.t in the Perl source directory:
srand 123456;$-=rand$_--=>@[[$-,$_]=@[[$_,$-]for(reverse+1..(@[=split //=>"IGrACVGQ\x02GJCWVhP\x02PL\x02jNMP"));print+(map{$_^q^"^}@[),"\n" SKIP: Solaris specific.
which is skipped when running the test, because it's "Solaris specific" - or at least, it claims to be so. And the only thing that's possibly system specific in the above Japh is the use of srand/rand.