feat: allow using setup-cpp as a library

fix: pin vcpkg on Alpine Arm64

On MacOS, the LLVM binaries could conflict with the system libraries. It's better to intentionally use the LLVM binaries.

Now, `LLVM_DYLD_LIBRARY_PATH` and `LLVM_LD_LIBRARY_PATH` are used instead of `DYLD_LIBRARY_PATH` and `LD_LIBRARY_PATH`.

In bashrc, after sourcing cpprc, you could
```shell
export LD_LIBRARY_PATH="$LLVM_LD_LIBRARY_PATH;$LD_LIBRARY_PATH"
export DYLD_LIBRARY_PATH="$LLVM_DYLD_LIBRARY_PATH;$DYLD_LIBRARY_PATH"
```

fix: do not add LLVM libraries to dyld by default