Link LLVM dynamically on aarch64-apple-darwin dist

[sgasho]

retry after: #154485

create a symlink from libLLVM-.....dylib to libLLVM.dylib in dist.rs

[bjorn3]

It looks like we are actually forcing the unversioned name to be used at another place:

rust/src/bootstrap/src/core/build_steps/dist.rs

Lines 2488 to 2499 in f92020a

	// On macOS, rustc (and LLVM tools) link to an unversioned libLLVM.dylib
	// instead of libLLVM-11-rust-....dylib, as on linux. It's not entirely
	// clear why this is the case, though. llvm-config will emit the versioned
	// paths and we don't want those in the sysroot (as we're expecting
	// unversioned paths).
	if target.contains("apple-darwin") && builder.llvm_link_shared() {
	let src_libdir = builder.llvm_out(target).join("lib");
	let llvm_dylib_path = src_libdir.join("libLLVM.dylib");
	if llvm_dylib_path.exists() {
	builder.install(&llvm_dylib_path, dst_libdir, FileType::NativeLibrary);
	}
	!builder.config.dry_run()

Would removing that instead work?

[sgasho]

Yes, I checked that removing it produces libLLVM.dylib and libLLVM-.dylib, and ./x build did not fail. So it seems it worked.
However, ZuseZ4 and I discussed that we should prepare both versioned and unversioned libLLVM by COPYING first, not symlink.

Two biggest reasons are

1. Multiple people said that copying libLLVM with the versioned name worked: ./x build failed with llvm-config: error: libLLVM-22-rust-1.96.0-nightly.dylib is missing #154408 (comment)
2. Nokel81 said that symlink did not work for him: ./x build failed with llvm-config: error: libLLVM-22-rust-1.96.0-nightly.dylib is missing #154408 (comment)

for 2, ln -s command that Nokel81 posted on the comment has a typo in the extension part. But we have no idea whether the symlink itself actually failed or whether the command was just pasted incorrectly. It's possible that my method for verifying symlinks is incorrect.

So, we get to land copying PR first, then this symlink later on.

[bjorn3]

So, we get to land copying PR first, then this symlink later on.

With my suggestion there wouldn't be any symlink either, right? It would just be removing the special case for macOS such that everything is handled the same way as it is handled on Linux.

[sgasho]

mmm...symlink has been created. I think I'm misunderstanding something.

Is something wrong with the image below? like, I'm looking at a wrong directory, or....

Would removing that instead work?

Am I misunderstanding this, or verification steps have some mistakes(#154986 (comment))