runtime: consolidate function descriptor definitions on PPC64
This reapplies CL 481075, which was a reappliation of CL 478917.
This CL has been reverted twice now due to conflicts with CL 392854 /
CL 481061, which had bugs and had to be reverted.
Now this CL skips the conflicting changes to runtime/cgo/asm_ppc64x.s,
which will be merged directly into a new version of CL 392854 /
CL 481061. That way, if there are _more_ issues, this CL need not be
involved in any more reverts.
Change-Id: I2801b918faf9418dd0edff19f2a63f4d9e08896c
Reviewed-on: https://go-review.googlesource.com/c/go/+/485335
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>