internal/rosa: make build script executable

This makes it slightly easier to invoke when working on a package via --enter.

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

internal/rosa/rosa.go

@@ -197,9 +197,12 @@ func fixupEnviron(env, extras []string, paths ...string) []string {
 	return append(extras, env...)
 }
 
+// scriptName is the name of the fixed-up build script.
+const scriptName = "all"
+
 // absCureScript is the absolute pathname [Toolchain.New] places the fixed-up
 // build script under.
-var absCureScript = AbsSystem.Append(".cure-script")
+var absCureScript = AbsSystem.Append(scriptName)
 
 const (
 	// TExclusive denotes an exclusive [pkg.Artifact].
@@ -310,15 +313,19 @@ mkdir -vp /work/system/bin
 		flag&THostNet != 0,
 		flag&TExclusive != 0,
 		fhs.AbsRoot, env,
-		AbsSystem.Append("bin", "sh"),
+		absCureScript,
-		[]string{"sh", absCureScript.String()},
+		nil,
 
 		slices.Concat([]pkg.ExecPath{pkg.Path(
 			fhs.AbsRoot, true,
 			support...,
 		), pkg.Path(
 			absCureScript, false,
-			pkg.NewFile(".cure-script", []byte("set -eu -o pipefail\n"+script)),
+			pkg.NewFile(scriptName, []byte(
+				"#!/system/bin/sh\n"+
+					"set -eu -o pipefail\n"+
+					script,
+			)),
 		)}, paths)...,
 	)
 }