[Gm2] libpth source added to gm2 libraries

[Gaius Mulley]

Hello,

I've just checked in a number of changes which include the libpth source
as one of the Modula-2 libraries to be built and installed.  There is
still work to be done to make it configurable (disable/enable and detect
a system version etc).  But currently I think it should build locally and be
able to run the tests locally (in the build tree).

The major reasons I've added pth to the libraries is that the last
release of libpth was in 2007 and also that Redhat/Fedora systems have
dropped libpth.  The alternative threading libraries don't have the
micro-context primitives which GNU Pth provides (used for coroutines).

It will be easy enough to disable the building of this extra library
- hopefully this will be achieved over the next couple of days.

I've built gm2 on a linaro arm board and also a amd64 system, if anyone
has access to a Fedora or Redhat system - I'd be very interested to hear
how these changes fare.  The tests are currently running on the linaro
arm machine.

The changes are to the gcc-8.2.0 branch of gm2,


regards,
Gaius