runtime: on linux/PPC64, usleep computes incorrect tv_nsec parameter [1.19 backport]

[gopherbot]

@pmur requested issue #56374 to be considered for backport to the next 1.19 minor release.

@gopherbot please consider a backport to 1.18 and 1.19. This is a subtle bug.

[gopherbot]

Change https://go.dev/cl/445157 mentions this issue: [release-branch.go1.19] runtime: fix usleep on linux/PPC64

[gopherbot]

Closed by merging 23fd10b to release-branch.go1.19.