internal/rosa: read-only access to built-ins

This removes potential footguns caused by mutable builtins without requiring unnecessary clones.

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

internal/rosa/llvm.go

@@ -48,7 +48,7 @@ func litArgs(verbose bool, skipChecks ...string) string {
 }
 
 func init() {
-	native.MustRegister("llvm", func(t Toolchain) (*Metadata, pkg.Artifact) {
+	builtin.MustRegister("llvm", func(t Toolchain) (*Metadata, pkg.Artifact) {
 		meta := Metadata{
 			Name:        "llvm",
 			Description: "a collection of modular and reusable compiler and toolchain technologies",
@@ -168,7 +168,7 @@ func init() {
 				)
 			}
 
-			if t.opts&OptLLVMNoLTO == 0 {
+			if t.opts&OptToolchainLTO != 0 {
 				cache = append(cache, []KV{
 					// very expensive
 					{"LLVM_ENABLE_LTO", "Thin"},