$ spack spec netcdf-fortran %pgi ^netcdf+mpi ^openssl%gcc
Input spec
------------------------------
  netcdf-fortran%pgi
      ^netcdf+mpi
      ^openssl%gcc

Normalized
------------------------------
  netcdf-fortran%pgi
      ^netcdf+mpi
          ^curl
              ^openssl%gcc
                  ^zlib
          ^m4

Concretized
------------------------------
  netcdf-fortran@4.4.4%pgi@16.5-0 arch=linux-centos6-x86_64
      ^netcdf@4.4.1%pgi@16.5-0+hdf4+mpi arch=linux-centos6-x86_64
          ^curl@7.50.1%pgi@16.5-0 arch=linux-centos6-x86_64
              ^openssl@1.0.2h%gcc@6.1.0 arch=linux-centos6-x86_64
                  ^zlib@1.2.8%pgi@16.5-0 arch=linux-centos6-x86_64
          ^hdf@4.2.11%pgi@16.5-0+szip arch=linux-centos6-x86_64
              ^jpeg@9b%pgi@16.5-0 arch=linux-centos6-x86_64
              ^szip@2.1%pgi@16.5-0 arch=linux-centos6-x86_64
          ^hdf5@1.10.0-patch1%pgi@16.5-0+cxx~debug+fortran+mpi+shared+szip~threadsafe arch=linux-centos6-x86_64
              ^mvapich2@2.2b%pgi@16.5-0~debug~gforker+hydra~mrail~nemesis~nemesisib~nemesisibtcp+psm~remshell~slurm~sock arch=linux-centos6-x86_64
                  ^libpciaccess@0.13.4%pgi@16.5-0 arch=linux-centos6-x86_64
                      ^libtool@2.4.6%pgi@16.5-0 arch=linux-centos6-x86_64
                          ^m4@1.4.17%pgi@16.5-0+sigsegv arch=linux-centos6-x86_64
                              ^libsigsegv@2.10%pgi@16.5-0 arch=linux-centos6-x86_64

$ spack spec netcdf-fortran %pgi ^netcdf+mpi ^openssl%gcc ^libpciaccess%pgi
Input spec
------------------------------
  netcdf-fortran%pgi
      ^libpciaccess%pgi
      ^netcdf+mpi
      ^openssl%gcc

Normalized
------------------------------
==> Error: netcdf-fortran does not depend on libpciaccess