internal/rosa/llvm: use llvm build system

This removes the multistep bootstrap hack. Stage0 exceptions are also eliminated for a later change to bring the stage0 distribution down to just a bare toolchain, toybox and shell. This change also enables dynamic linking and ThinLTO.

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

internal/rosa/all.go

@@ -16,9 +16,7 @@ import (
 type PArtifact int
 
 const (
-	CompilerRT PArtifact = iota
-	LLVMRuntimes
-	Clang
+	LLVM PArtifact = iota
 
 	// EarlyInit is the Rosa OS init program.
 	EarlyInit
@@ -77,7 +75,6 @@ const (
 	LibXau
 	Libbsd
 	Libcap
-	Libclc
 	Libdrm
 	Libev
 	Libexpat
@@ -174,12 +171,13 @@ const (
 	// PresetUnexportedStart is the first unexported preset.
 	PresetUnexportedStart
 
-	llvmSource = iota - 1
-	buildcatrust
+	buildcatrust = iota - 1
 	utilMacros
 
 	// Musl is a standalone libc that does not depend on the toolchain.
 	Musl
+	// muslHeaders is a system installation of [Musl] headers.
+	muslHeaders
 
 	// gcc is a hacked-to-pieces GCC toolchain meant for use in intermediate
 	// stages only. This preset and its direct output must never be exposed.