foreach ($firstbuild, @otherbuilds)
{
    system (qq(C:/execu $_ file.c));
}

##</code><code>##

open (OUT, ">cmd.txt") || die "$!\n";
foreach ($firstbuild, @otherbuilds)
{
    print OUT "C:/execu $_ file.c\n";
}
close OUT;
system ("cmd.txt");