#error checking, use... omitted
#may have typos - read as perl-ish pseudocode

my @buildirs = ("foo1", "foo2");
my $repo="myrepo"; 
my $startdir=File::Spec::curdir();

foreach my $buildme (@buildirs) {
   chdir($buildme); 
   symlink($repo, "lib");
   system("perl Build.PL");
   unlink("lib");
}
chdir($startdir);