[llvm] [objcopy] Implement --weaken, --weaken-symbol(s) flags for MachO Object Files (PR #70560)

[Fangrui Song via llvm-commits]

================
@@ -94,6 +94,14 @@ static void updateAndRemoveSymbols(const CommonConfig &Config,
                                    const MachOConfig &MachOConfig,
                                    Object &Obj) {
   for (SymbolEntry &Sym : Obj.SymTable) {
+    // Weaken first to match ELFObjcopy behavior
----------------
MaskRay wrote:

`Weaken symbols first to match ELFObjcopy behavior.`

https://github.com/llvm/llvm-project/pull/70560