internal/rosa: expose supported architectures

This information is useful to external tooling and makes a lot more sense in this package than cmd/mbf. This change also fixes non-native artifact resolution during clean.

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

cmd/mbf/main.go

@@ -883,13 +883,19 @@ func main() {
 			func([]string) error {
 				return cm.Do(func(cache *pkg.Cache) error {
 					t := rosa.Native().Clone().Std()
-					a := t.Append(nil, t.CollectAll()...)
-					for arch := range pkg.Arch() {
+					handles := t.CollectAll()
+
+					flags := t.Flags()
+					a := t.Append(nil, handles...)
+					for arch := range rosa.Arches(nil) {
 						if arch == runtime.GOARCH {
 							continue
 						}
-						t.DropCaches(arch, t.Flags())
-						a = t.Append(a, t.CollectAll()...)
+
+						t.DropCaches(arch, rosa.OptLLVMNoLTO|rosa.OptSkipCheck)
+						a = t.Append(a, handles...)
+						t.DropCaches(arch, flags)
+						a = t.Append(a, handles...)
 					}
 
 					ids, checksums, err := cache.Clean(