rustdoc: Use `unix_sigpipe` instead of `rustc_driver::set_sigpipe_handler`
Do what was already done for `rustc` in #102587, namely start using `unix_sigpipe` instead of `rustc_driver::set_sigpipe_handler`.
After this has been merged, we can completely remove `rustc_driver::set_sigpipe_handler`.
PR that added `set_sigpipe_handler`: https://github.com/rust-lang/rust/pull/49606
Tracking issue for `unix_sigpipe`: #97889
Verification of this change
---------------------------
1. Remove `#[unix_sigpipe = "sig_dfl"]`
1. Run `./x.py build`
1. Run `./build/aarch64-apple-darwin/stage1/bin/rustdoc --help | false`
1. Observe ICE
1. Add back `#[unix_sigpipe = "sig_dfl"]`
1. Run `./x.py build`
1. Run `./build/aarch64-apple-darwin/stage1/bin/rustdoc --help | false`
1. Observe ICE fixed
``@rustbot`` labels +T-rustdoc
d0ffd20a75