Rollup merge of rust-lang#77328 - hyd-dev:assert-to-rtassert, r=Amanieu

Use `rtassert!` instead of `assert!` from the child process after fork() in std::sys::unix::process::Command::spawn()

As discussed in rust-lang#73894, `assert!` panics on failure, which is not signal-safe, and `rtassert!` is a suitable replacement.

Fixes rust-lang#73894.

r? @Amanieu @cuviper @joshtriplett

Author: jonas-schievink

std/src/sys/unix/process/process_unix.rs

@@ -67,7 +67,7 @@ impl Command {
                     // pipe I/O up to PIPE_BUF bytes should be atomic, and then
                     // we want to be sure we *don't* run at_exit destructors as
                     // we're being torn down regardless
-                    assert!(output.write(&bytes).is_ok());
+                    rtassert!(output.write(&bytes).is_ok());
                     libc::_exit(1)
                 }
                 n => n,