[release-branch.go1.11] runtime: skip stack barrier copy when there are no pointers
After CL 31455, "go fun(n)" may put "n" to write barrier buffer
when there are no pointers in fun's arguments.
Updates #29565
Change-Id: Icfa42b8759ce8ad9267dcb3859c626feb6fda381
Reviewed-on: https://go-review.googlesource.com/c/155779
Reviewed-by: Keith Randall <khr@golang.org>
(cherry picked from commit
5372257e600989ab4cf742b35e3fa649cad3f45c)
Reviewed-on: https://go-review.googlesource.com/c/156357
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>