internal/rosa: remove legacy exec helper

This change also adds a fourth stage to the bootstrap machinery, offering more correct toolchain validation that works around LLVM dynamic linking flaws.

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

cmd/mbf/main.go

@@ -616,7 +616,7 @@ func main() {
 
 	{
 		c.NewCommand(
-			"stage3",
+			"stage4",
 			"Check for toolchain 3-stage non-determinism",
 			func(args []string) (err error) {
 				var (
@@ -636,21 +636,31 @@ func main() {
 
 				if err = cm.Do(func(cache *pkg.Cache) (err error) {
 					_, llvm := rosa.Native().New(rosa.Std - 1).Load(_llvm)
-					pathname, checksum[0], err = cache.Cure(llvm)
+					pathname, _, err = cache.Cure(llvm)
 					return
 				}); err != nil {
 					return
 				}
 				log.Println("stage2:", pathname)
+
 				if err = cm.Do(func(cache *pkg.Cache) (err error) {
 					_, llvm := rosa.Native().New(rosa.Std).Load(_llvm)
-					pathname, checksum[1], err = cache.Cure(llvm)
+					pathname, checksum[0], err = cache.Cure(llvm)
 					return
 				}); err != nil {
 					return
 				}
 				log.Println("stage3:", pathname)
 
+				if err = cm.Do(func(cache *pkg.Cache) (err error) {
+					_, llvm := rosa.Native().New(rosa.Stage3).Load(_llvm)
+					pathname, checksum[1], err = cache.Cure(llvm)
+					return
+				}); err != nil {
+					return
+				}
+				log.Println("stage4:", pathname)
+
 				if checksum[0] != checksum[1] {
 					err = &pkg.ChecksumMismatchError{
 						Got:  checksum[0].Value(),
@@ -658,7 +668,7 @@ func main() {
 					}
 				} else {
 					log.Println(
-						"stage2 is identical to stage3",
+						"stage3 is identical to stage4",
 						"("+pkg.Encode(checksum[0].Value())+")",
 					)
 				}