internal/rosa: create /bin symlinks via helper

This centralises the workaround for surprisingly common buggy scripts with nonstandard hardcoded paths.

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

internal/rosa/rosa.go

@@ -414,6 +414,10 @@ type PackageAttr struct {
 
 	// Passed to [Toolchain.NewPatchedSource].
 	Patches []KV
+	// Programs to make available in /bin/.
+	Bin []string
+	// Whether to replace /usr/bin/ with a symlink to /bin/.
+	PopulateUsrBin bool
 
 	// Unregistered extras.
 	Extra []pkg.Artifact
@@ -544,6 +548,26 @@ cd '/usr/src/` + name + `/'
 		})
 	}
 
+	bin := attr.Bin
+	if attr.PopulateUsrBin {
+		scriptEarly += `
+chmod +w /usr/ /usr/bin/
+rm -rf /usr/bin/
+ln -s ../bin /usr/`
+		bin = append(bin, "env")
+	}
+
+	if t.stage != stageGentoo && len(bin) > 0 {
+		scriptEarly += "\nchmod +w /bin/" +
+			"\n(set -o braceexpand && ln -sf ../system/bin/"
+		if len(bin) > 1 {
+			scriptEarly += "{'" + strings.Join(bin, "','") + "'}"
+		} else {
+			scriptEarly += "'" + bin[0] + "'"
+		}
+		scriptEarly += " /bin/)\n"
+	}
+
 	return t.New(
 		rn,
 		attr.Flag,