[llvm] [llvm-ar] --help: fix unquoted angle bracket (PR #101364)

[James Henderson via llvm-commits]

jh7370 wrote:

Done. Please keep an eye open for build bot failure notifications (I wouldn't expect this PR to trigger any that are actually related, but still it's worth being cautious).

https://github.com/llvm/llvm-project/pull/101364