runtime: openbsd fork-exec calls exit instead of _exit in failed child

[rsc]

As part of work on CL 459176 I noticed that the libc ports are calling exit(3) instead of _exit(2). I fixed Darwin in that CL but did not want to touch OpenBSD so close to the release if it wasn't obviously broken. Probably a bad atexit handler could foul up the fork child, and _exit should be used instead. Needs investigation and probably a fix.

[dmitshur]

CC @golang/openbsd.

[gopherbot]

Change https://go.dev/cl/459176 mentions this issue: runtime: call __fork instead of fork on darwin

[gopherbot]

Change https://go.dev/cl/459178 mentions this issue: runtime: call __fork instead of fork on darwin

[gopherbot]

Change https://go.dev/cl/459178 mentions this issue: [release-branch.go1.19] runtime: call __fork instead of fork on darwin

[gopherbot]

Change https://go.dev/cl/459179 mentions this issue: [release-branch.go1.18] runtime: call __fork instead of fork on darwin