runtime: fix breakpoint in ppc64x
runtime: fix breakpoint in ppc64x

Currently runtime.Breakpoint generates a SIGSEGV in ppc64.
The solution is an unconditional trap similar to what clang and gcc do. It is documented in the section C.6 of the ABI Book 3.

Fixes #52101

Change-Id: I071d2f2679b695ef268445b04c9222bd74e1f9af
GitHub-Last-Rev: fff4e5e8ffe23bf0cef135b22abd2cc0a3838613
GitHub-Pull-Request: golang/go#52102
Reviewed-on: https://go-review.googlesource.com/c/go/+/397554
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Paul Murphy <2e1d8d6f81223fe22f04c5349bc2b02555a275af@ibm.com>
Run-TryBot: Paul Murphy <2e1d8d6f81223fe22f04c5349bc2b02555a275af@ibm.com>
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

golang/go,nawawi/go,golang/go,golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go,nawawi/go,golang/go,golang/go,golang/go,nawawi/go,nawawi/go,golang/go,nawawi/go