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>

internal/rosa/make.go

@@ -52,15 +52,16 @@ type MakeHelper struct {
 var _ Helper = new(MakeHelper)
 
 // extra returns make and other optional dependencies.
-func (attr *MakeHelper) extra(flag int) P {
-	extra := P{_make}
-	if (attr == nil || !attr.OmitDefaults) && flag&TEarly == 0 {
-		extra = append(extra,
+func (attr *MakeHelper) extra() P {
+	if attr == nil || !attr.OmitDefaults {
+		return P{
+			_make,
+
 			_awk,
 			_coreutils,
-		)
+		}
 	}
-	return extra
+	return P{_make}
 }
 
 // wantsChmod returns whether the build system needs to be generated.