internal/rosa: flags for toolchain-dependent artifact

This is much cleaner to add extra flags to.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa.go

@@ -175,10 +175,15 @@ func fixupEnviron(env, extras []string, paths ...string) []string {
 // build script under.
 var absCureScript = fhs.AbsUsrBin.Append(".cure-script")
 
+const (
+	// TExclusive denotes an exclusive [pkg.Artifact].
+	TExclusive = 1 << iota
+)
+
 // New returns a [pkg.Artifact] compiled on this toolchain.
 func (t Toolchain) New(
 	name string,
-	exclusive bool,
+	flag int,
 	extra []pkg.Artifact,
 	checksum *pkg.Checksum,
 	env []string,
@@ -219,7 +224,7 @@ func (t Toolchain) New(
 		args[0] = "bash"
 		support = slices.Concat([]pkg.Artifact{
 			cureEtc{},
-			toolchainBusybox.New("stage3-"+version, false, nil, nil, nil, `
+			toolchainBusybox.New("stage3-"+version, 0, nil, nil, nil, `
 tar -C /work -xf /usr/src/stage3.tar.xz
 rm -rf /work/dev/ /work/proc/
 ln -vs ../usr/bin /work/bin
@@ -272,7 +277,7 @@ ln -vs ../usr/bin /work/bin
 	}
 
 	return pkg.NewExec(
-		name, checksum, pkg.ExecTimeoutMax, exclusive,
+		name, checksum, pkg.ExecTimeoutMax, flag&TExclusive != 0,
 		fhs.AbsRoot, env,
 		path, args,
 
@@ -321,7 +326,7 @@ cat /usr/src/` + name + `-patches/* | \
 `
 		aname += "-patched"
 	}
-	return t.New(aname, false, stage3Concat(t, []pkg.Artifact{},
+	return t.New(aname, 0, stage3Concat(t, []pkg.Artifact{},
 		t.Load(Patch),
 	), nil, nil, script, paths...)
 }