OpenFAST build errors on macOS missing MPI symbols when building as shared library

[jrood-nrel]

I'm seeing these errors during the 99% linking phase when building on macOS with OpenMPI 3.1.3:

Undefined symbols for architecture x86_64:
  "_MPI_Allreduce", referenced from:
      fast::OpenFAST::fillScInputsGlob()     in OpenFAST.cpp.o
  "_MPI_Comm_create", referenced from:
      fast::OpenFAST::allocateMemory()     in OpenFAST.cpp.o
  "_MPI_Comm_free", referenced from:
      fast::OpenFAST::end()    in OpenFAST.cpp.o
  "_MPI_Comm_group", referenced from:
      fast::OpenFAST::setInputs(fast::fastInputs const&) in OpenFAST.cpp.o
  "_MPI_Comm_rank", referenced from:
      fast::OpenFAST::allocateMemory()     in OpenFAST.cpp.o
      fast::OpenFAST::setInputs(fast::fastInputs const&) in OpenFAST.cpp.o
  "_MPI_Comm_size", referenced from:
      fast::OpenFAST::allocateTurbinesToProcsSimple()     in OpenFAST.cpp.o
  "_MPI_Group_free", referenced from:
      fast::OpenFAST::end()    in OpenFAST.cpp.o
  "_MPI_Group_incl", referenced from:
      fast::OpenFAST::allocateMemory()     in OpenFAST.cpp.o
  "_ompi_mpi_comm_null", referenced from:
      fast::OpenFAST::end()    in OpenFAST.cpp.o
      fast::OpenFAST::fillScInputsGlob()     in OpenFAST.cpp.o
      fast::OpenFAST::allocateMemory()     in OpenFAST.cpp.o
  "_ompi_mpi_double", referenced from:
      fast::OpenFAST::fillScInputsGlob()     in OpenFAST.cpp.o
  "_ompi_mpi_op_sum", referenced from:
      fast::OpenFAST::fillScInputsGlob()     in OpenFAST.cpp.o
ld: symbol(s) not found for architecture x86_64

I will update this when I test whether or not OpenMPI 1.10.4 still works, which was previously known to work.

[jrood-nrel]

Same errors on macOS with OpenMPI 1.10.4 which worked previously before I had to temporarily shut off Nalu testing on the Mac.

[jrood-nrel]

With the help of @gantech I was able to build this now. I just have to figure out what I was doing wrong previously.

[jrood-nrel]

@gantech I found the difference in what I was doing originally that causes this problem. If I add -DBUILD_SHARED_LIBS:BOOL=ON to build OpenFAST as a shared library, that's what is causing my issue. It was building statically by default and I just realized this.

[jrood-nrel]

More specifically it's clearly missing linking to libmpi on the link line when I build as a shared library where libmpi is on the link line when I build as static.

[gantech]

Thanks @jrood-nrel. I'll try to add the link to libmpi for building the library as well.

[rafmudaf]

fixed by #242