runtime: crash on linux-ppc64le [1.20 backport]

[gopherbot]

@laboger requested issue #59196 to be considered for backport to the next 1.20 minor release.

@gopherbot please open the backport tracking issues for Go 1.20 and 1.19. This is an assembler regression that results in a serious error and has no workaround.

[gopherbot]

Change https://go.dev/cl/479475 mentions this issue: cmd/internal/obj/ppc64: fix incorrect base reg causing segv

[gopherbot]

Change https://go.dev/cl/479535 mentions this issue: [release-branch.go1.20] cmd/internal/obj/ppc64: fix incorrect base reg causing segv

[laboger]

This is a serious issue in the assembler in which generates an instruction that uses r0 as the base register. The result is a segv if that instruction is executed. There is no workaround. Refer to the original issue for further detail.
(The second CL listed here has been abandoned. It was incorrectly created when I tried to resolve merge problems with the first cherry-pick.)

[gopherbot]

Closed by merging 9a164d1 to release-branch.go1.20.