CL 108095 goes to some length inorder to keep the stack usage of getHPETTimecounter code paths bellow a limit
being checked by the linker analysis. That limit is spurious, when running on the system or signal stack.

In a similar scenario, cgocallback_gofunc performs an indirect call through AX to hide the call from the linker analysis.
Here instead, mark getHPETTimecounter //go:systemstack and call it appropriately.

Change-Id: I80bec5e4974eee3c564d94f6e1142f322df88b2f
Reviewed-on: https://go-review.googlesource.com/111495
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>