ENH: support libz disabling via WM_COMPILE_CONTROL (as ~libz)

- eg, for partially incomplete systems (without libz devel header)

ENH: clearer binding of dummy Pstream in OpenFOAM/Make/options

- link of dummy stub Pstream now contingent on linking libOpenFOAM as
  well. This makes the purpose slightly clearer

ENH: cleaner option naming/handling in wmake script

- allow special purpose -no-openfoam option.
  Eg, compiling test programs without OpenFOAM and Pstream libraries
  but using the rest of the wmake system.

ENH: add +openmp support into WM_COMPILE_CONTROL (#2633)

- this adds compile/link flags for openmp.
  For single-use, can also use 'wmake -openmp'.

  If both +openmp and ~openmp are specified in WM_COMPILE_CONTROL
  the ~openmp will have priority.

  This is actually done indirectly since ~openmp will set empty
  COMP_OPENMP, LINK_OPENMP internal variables, which the +openmp then
  adds to the c++FLAGS and linkexe targets (ie, won't actually add
  anything).

ENH: add +ccache or ccache=... ...