runtime: call cgocallbackg indirectly

cgocallback calls cgocallbackg after switching the stack. Call it
indirectly to bypass the linker's nosplit check.

Apparently (at least on Windows) cgocallbackg can use quite a bit
stack space in a nosplit chain. We have been running over the
nosplit limit, or very close to the limit. Since it switches
stack in cgocallback, it is not meaningful to count frames above
cgocallback and below cgocallbackg together. Bypass the check.

For #45658.

Change-Id: Ie22017e3f82d2c1fcc37336696f2d02757856399
Reviewed-on: https://go-review.googlesource.com/c/go/+/312669


Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>