runtime: "runtime·lock: lock count" fatal error when cgo is enabled [1.18 backport]

[gopherbot]

@prattmic requested issue #56243 to be considered for backport to the next 1.18 minor release.

@gopherbot Please backport to 1.18 and 1.19

This issue is not new but can cause random memory corruption in any program that has a goroutine exit with LockOSThread set.

[gopherbot]

Change https://go.dev/cl/443816 mentions this issue: [release-branch.go1.18] runtime: always keep global reference to mp until mexit completes

[gopherbot]

Closed by merging 2c2952a to release-branch.go1.18.