internal/cpu, runtime: add S/390 CPU capability support

Patch by Robin Dapp.

Updates https://gcc.gnu.org/PR89123

Change-Id: I4d1583747111b7446eb63aade3612df669ac1ed1
Reviewed-on: https://go-review.googlesource.com/c/162887
Reviewed-by: Ian Lance Taylor <iant@golang.org>
3 files changed