d01648b60e
Do not attempt to unlock envlock in child process after a fork. This implements the first two points from https://github.com/rust-lang/rust/issues/64718#issuecomment-793030479 This is a breaking change for cases where the environment is accessed in a Command::pre_exec closure. Except for single-threaded programs these uses were not correct anyway since they aren't async-signal safe. Note that we had a ui test that explicitly tried `env::set_var` in `pre_exec`. As expected it failed with these changes when I tested locally.