internal/rosa/llvm: migrate runtimes and clang

This eliminates most newLLVM family of functions.

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

internal/rosa/stage0.go

@@ -7,12 +7,11 @@ import (
 )
 
 func (t Toolchain) newStage0() (pkg.Artifact, string) {
-	runtimes, clang := t.NewLLVM()
 	return t.New("rosa-stage0", 0, []pkg.Artifact{
 		t.Load(Musl),
 		t.Load(LLVMCompilerRT),
-		runtimes,
-		clang,
+		t.Load(LLVMRuntimes),
+		t.Load(LLVMClang),
 
 		t.Load(Zlib),
 		t.Load(Bzip2),