Shared libraries on ppc64le will require a larger minimum stack frame (because
the ABI mandates that the TOC pointer is available at 24(R1)). Part 2b of
preparing for that is to have all the code in the linker that needs to know
this size of this call a function to find out.

Change-Id: I246363840096db22e44beabbe38b61d60c1f31ad
Reviewed-on: https://go-review.googlesource.com/15675Reviewed-by: Ian Lance Taylor <iant@golang.org>