- if FOAM_EXT_LIBBIN is unset and some scripts set this to /usr/lib*
  as a fallback (eg, to avoid an undefined value) this will cause a
  system library to be found before appropriate *_ARCH_PATH entry.

  This was noticed during a scotch compilation without third-party:
  resulting in the system library (/usr/lib64/libscotch.so) to be found
  instead of the SCOTCH_ARCH_PATH location
  (/usr/lib64/mpi/gcc/openmpi/lib64/).

  Simply changing the search order doesn't work for use, since we wish
  to retain a preference for any dynamic libraries discovered in a
  real FOAM_EXT_LIBBIN.

  Circumvent these issues by only taking libraries from
  FOAM_EXT_LIBBIN if it also points to a location within ThirdParty.