MacOS Homebrew fixes, Windows fix

[BUG FIX]

• On MacOS with homebrew, the homebrew provided gfortran does not
  search the homebrew lib dirs for the X11 libraries, while the system
  clang does, so the latter could find them, but the former couldn't.

• Linking is failing on some Windows systems due to mismatch between
  Fortran and C naming conventions. Attempted fix applied.

Fix link pkg-config link dependency order

move Fortran library dependencies from cpgplot.pc to pgplot.pc

The Fortran library dependencies were erroneously put in the Libs
entry in cpgplot.pc rather than pgplot.pc.  This didn't affect
the internal tests.

However, the result was that -lgfortran was placed before -lpgplot
(for example), and on systems which perform single pass symbol lookup
during linking (e.g. most recent Linux boxes), the symbols in gfortran
which were required by pgplot were never resolved.

5.2.2-7

Now builds on Windows via MSYS2.

pgplot-5.2.2-7.tar.gz is the end-user source distribution (the others are for developers)

5.2.2-6

forgot to bump the version