OpenMP for both clang and GCC, part III

Why am I doing this? To support OpenMP for base-clang and ports-gcc.

Why all these patches? When OpenMP is supported, patched ports/ can build
correctly, leaving OpenMP disabled for those ports. Afterwards,
porters can choose to enable it.

What next? Hopefully, patches to disable OpenMP for a few ports are
all applied, followed by a patch to ports-gcc and a new libomp (or
update to base-clang) for clang.

These last two steps result in OpenMP working on clang and gcc-ports
compilers when requested. Otherwise, no unexpected behaviours in ports.

Other questions:

Is OpenMP faster? Yes, for code written for it. OpenMP applies multiple
cores to one code fragment resulting in clear speedup. If the code is
good (and there are bad examples out there) it is correct and faster.

Is it stable? Since it is userland, and OpenMP implementations elsewhere
are stable, very likely so on OpenBSD.

Does it rely on kernel SMP? No. It's pthreads but the code is
simpler to read and write.

Does it work properly on OpenBSD? Some GNU configure scripts assume that
if it is present that therefore it should be used. Nope. Patches will fix
that. Otherwise, for packages like z3, sample boost/odeint, it does
work faster on OpenBSD at runtime. Things will need some testing before
it should be enabled on a per-port basis.

How did you create these patches?

I've checked (tested on amd64) many of the ports for OpenBSD -current:
- all github-hosted ports
- all pypi-hosted ports
- all astro/ audio/ cad/ devel/ math/ multimedia/ security/ ports

I have assumed that scripting languages and related packages
do not use OpenMP. Languages such as: ruby, perl, python,
php, lua. And ports such as go-, hs- (haskell), mono-.

Status:

The following have patches tested and published by me on amd64:

audio/clementine
audio/libsoxr
devel/gettext (applied by @naddy)
graphics/libraw
math/R (applied by @feinerer)
math/ecm
math/fftw
math/fftw3
math/z3 (applied by @rsadowski)

and

emulators/vbam discovered by Charlene; not applied

For supporting OpenMP by ports-gcc, I've published
a patch to PLIST to add the gcc OpenMP runtime libgomp.

For clang 8.0, I'll publish a package for the support library libomp.

(Smarter people than me can decide if such a new port is needed
or clang should have built-in OpenMP support. And when.)

The following packages already have OpenMP turned off as indicated.
This is specifically; by an OpenBSD patch; or by default:

archivers/zstd defaulted
audio/soundtouch defaulted
audio/sox off
cad/ngspice defaulted
devel/bullet off
devel/cryptopp patched
geo/osrm-backend defaulted
graphics/darktable off
graphics/gd defaulted
graphics/lensfun defaulted
graphics/libmypaint defaulted
graphics/tesseract defaulted
math/mlpack defaulted
math/suitesparse defaulted
security/john defaulted
security/john-jumbo defaulted


The following are source code packages (header files or modules)
and while they support OpenMP this is up to the user (programmer)
to choose to enable. So don't turn on or off::

math/armadillo
math/boost (specifically odeint)
math/eigen3