- specify any of these
./Allwmake -build-root=...
wmake -build-root=...
FOAM_BUILDROOT=... wmake
these specify an alternative root where build artifacts are to land.
Currently only used as an alternative for the 'build/' hierarchy
since the 'platforms/' target normally includes inputs as well.
Possible use:
```
(
export WM_MPLIB="%{foam_mplib}"
export FOAM_MPI="%{foam_mpi}"
export MPI_ARCH_PATH="%{mpi_prefix}"
export FOAM_BUILDROOT=/tmp/mpibuild
export FOAM_MPI_LIBBIN="$FOAM_BUILDROOT/platforms/$WM_OPTIONS/lib/$FOAM_MPI"
src/Pstream/Allwmake-mpi
)
```