plug-t-file-into-007-runtime

sub MAIN($file) {
    my $contents = slurp($file);
    my $basename = $file.IO.basename.subst(/".t" $/, "");
    my $tempfile-name = "$basename-$*PID.t";
    LEAVE { unlink $tempfile-name if $tempfile-name }
    signal(SIGINT).act: { unlink $tempfile-name if $tempfile-name; exit 1 }
    my $test-override = slurp("self-host/test-override");
    $contents .= subst(/^^ \h* "use _007::Test;" \h* $$/, $test-override);
    spurt($tempfile-name, $contents);

    my $failures = shell("perl6 $tempfile-name");
    $failures.exitcode; # to get rid of complaint when test file has failures
}