runtime: SIGSEGV on child side of fork pre-exec with -race on darwin/arm64 [1.26 backport]

[gopherbot]

@prattmic requested issue #79804 to be considered for backport to the next 1.26 minor release.

I believe this is a regression introduced in https://go.dev/cl/699177.

@gopherbot Please backport to 1.26. This is a regression that can cause random crashes with -race and os/exec.