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

[James Henderson via llvm-commits]

================
@@ -0,0 +1,89 @@
+# REQUIRES: x86-registered-target
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos %s -o %t
+
+# RUN: llvm-objcopy -W _func %t %t2
+# RUN: llvm-readobj --symbols %t2 | FileCheck %s -check-prefix=CHECK-1
+
+# CHECK-1:      Symbol {
+# CHECK-1-NEXT:   Name: _foo (1)
+# CHECK-1-NEXT:   Extern
+# CHECK-1-NEXT:   Type: Section (0xE)
+# CHECK-1-NEXT:   Section: __const (0x2)
+# CHECK-1-NEXT:   RefType: UndefinedNonLazy (0x0)
+# CHECK-1-NEXT:   Flags [ (0x0)
+# CHECK-1-NEXT:   ]
+# CHECK-1-NEXT:   Value: 0x0
+# CHECK-1-NEXT: }
+# CHECK-1-NEXT: Symbol {
+# CHECK-1-NEXT:   Name: _func (6)
+# CHECK-1-NEXT:   Extern
+# CHECK-1-NEXT:   Type: Section (0xE)
+# CHECK-1-NEXT:   Section: __text (0x1)
+# CHECK-1-NEXT:   RefType: UndefinedNonLazy (0x0)
+# CHECK-1-NEXT:   Flags [ (0x80)
+# CHECK-1-NEXT:     WeakDef (0x80)
+# CHECK-1-NEXT:   ]
+# CHECK-1-NEXT:   Value: 0x0
+# CHECK-1-NEXT: }
+
+# RUN: echo _foo > %t.rename.txt
+# RUN: echo _func >> %t.rename.txt
+# RUN: llvm-objcopy --weaken-symbols %t.rename.txt %t %t3
+# RUN: llvm-readobj --symbols %t3 | FileCheck %s -check-prefix=CHECK-2
+
+# CHECK-2:      Symbol {
+# CHECK-2-NEXT:   Name: _foo (1)
+# CHECK-2-NEXT:   Extern
+# CHECK-2-NEXT:   Type: Section (0xE)
+# CHECK-2-NEXT:   Section: __const (0x2)
+# CHECK-2-NEXT:   RefType: UndefinedNonLazy (0x0)
+# CHECK-2-NEXT:   Flags [ (0x80)
+# CHECK-2-NEXT:     WeakDef (0x80)
+# CHECK-2-NEXT:   ]
+# CHECK-2-NEXT:   Value: 0x0
+# CHECK-2-NEXT: }
+# CHECK-2-NEXT: Symbol {
+# CHECK-2-NEXT:   Name: _func (6)
+# CHECK-2-NEXT:   Extern
+# CHECK-2-NEXT:   Type: Section (0xE)
+# CHECK-2-NEXT:   Section: __text (0x1)
+# CHECK-2-NEXT:   RefType: UndefinedNonLazy (0x0)
+# CHECK-2-NEXT:   Flags [ (0x80)
+# CHECK-2-NEXT:     WeakDef (0x80)
+# CHECK-2-NEXT:   ]
+# CHECK-2-NEXT:   Value: 0x0
+# CHECK-2-NEXT: }
+
+## Verify --weaken-symbol plays nice with --redefine-sym
----------------
jh7370 wrote:

```suggestion
## Verify --weaken-symbol plays nice with --redefine-sym.
```

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