GNU readelf isn't available as consistently as I assumed across SunOS,
and it can be named different things on different illumos distros (some call
it readelf, others call it greadelf, etc), so it's safer to use elfdump.
This is a fairly easy fix, just kind of annoying.
Don't mark the .kPStaticModules section as relro for bfd, as the linkers on
Windows and Mac don't do this anyway.
Add a section insert of .kPStaticModules to config/expandlibs_exec.py, which
seems to be the primary cause of linking bustage on gold, lld, and mold.
