possible gcc optimizer issue

[Greg Troxel <gdt%lexort.com@localhost>]

I found that pkgsrc/geography/geos has test failures on netbsd-8
earmv7hf-el (RPI3).  Investigating, and asking others on pkgsrc-users to
test:

ok	netbsd-8	amd64
ok	netbsd-7	i386
ok	netbsd-7	amd64
ok      netbsd-current	sparc64

fail    netbsd-8        earmv7hf-el
fail    netbsd-current	earmv7hf-el

better*  netbsd-8        earmv7hf-el	-O0, instead of the default -O2

* by better, one test suite that had many failures with -O2 passes, and
  there is another error in a different suite that I currently believe
  is a different issue, and also seems more debuggable.

The geos tests pass on Linux arm and arm64.

So, it looks like either

  gcc on netbsd/arm is buggy

  geos has code that the standard says is undefined, and it happens to
  be ok except for arm/O2, or something like that

  something else I didn't think of


If I manage to isolate something of manageable size I'll post again;
geos is pretty big and complicated.