runtime: concurrent map read and map write with sync.RWMutex on ppc64le [1.25 backport]

[gopherbot]

@Jorropo requested issue #79186 to be considered for backport to the next 1.25 minor release.

cc @gopherbot please open backport issues for 1.25 and 1.26

This is a pretty bad correctness issue in concurrent code. It's hard to debug and has no easy workaround.

[gopherbot]

Change https://go.dev/cl/793880 mentions this issue: [release-branch.go1.25] cmd/compile,sync/atomic: make Add And & Or SQCST on PPC64

[gopherbot]

Change https://go.dev/cl/793881 mentions this issue: [release-branch.go1.25] cmd/compile,sync/atomic: make Add And & Or SQCST on PPC64