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/llvm.go

@@ -341,6 +341,13 @@ ln -s \
 
 		return &meta, t.NewPackage("llvm", meta.Version, source, &PackageAttr{
 			Flag: TExclusive,
+			Bin: []string{
+				"chmod",
+				"mkdir",
+				"rm",
+				"tr",
+				"awk",
+			},
 		}, &CMakeHelper{
 			Append: []string{"llvm"},
 
@@ -358,16 +365,7 @@ ln -s clang++ /work/system/bin/c++
 			// on 3-stage determinism to test later stages.
 			SkipTest: t.stage.isStage0(),
 
-			Test: `
-chmod +w /bin && ln -s \
-	../system/bin/chmod \
-	../system/bin/mkdir \
-	../system/bin/rm \
-	../system/bin/tr \
-	../system/bin/awk \
-	/bin
-ninja ` + jobsFlagE + ` check-all
-`,
+			Test: "ninja " + jobsFlagE + " check-all",
 		},
 			_python,
 			_perl,