[llvm-readtapi] Fix bad symlink with readtapi tool (#68835)

The Clang-AIX-Wyvern-Dev buildbot is currently failing at the set
directory permission due to a bad symlink caused by this
[commit](https://github.ibm.com/compiler/llvm-project/commit/a54f31fabd55ab111484b1e094e3d2c6b29c4715).
This change is creating the additional symlink `readtapi ->
llvm-readtapi` which causes it to appear in
`/buildbot_worker/official-worker/clang-aix-dev/installdir`.

After some investigation, it looks like `readtapi` is the only tool that
is getting symlinked that is not guarded by the
`LLVM_INSTALL_BINUTILS_SYMLINKS` macro. For example:

1. `llvm/tools/llvm-objcopy/CMakeLists.txt`

```
if(LLVM_INSTALL_BINUTILS_SYMLINKS)
  add_llvm_tool_symlink(objcopy llvm-objcopy)
endif()
```

2. `llvm/tools/llvm-dwp/CMakeLists.txt`
```
if(LLVM_INSTALL_BINUTILS_SYMLINKS)
  add_llvm_tool_symlink(dwp llvm-dwp)
endif()
```