message: allow downstream customers to provide their own mfem target
diff: @@ -137,7 +137,11 @@ endif()
  #------------------------------------------------------------------------------
  # MFEM
  #------------------------------------------------------------------------------
  -if (MFEM_DIR)
  +if (TARGET mfem)
  + # Case: included axom in project that also creates an mfem target, no need to recreate mfem
  + message(STATUS "MFEM support is ON, using existing mfem target")
  + blt_list_append(TO TPL_DEPS ELEMENTS mfem)
  +elseif (MFEM_DIR)
  include(cmake/thirdparty/FindMFEM.cmake)
  # If the CMake build system was used, a CMake target for mfem already exists
  if (NOT TARGET mfem)
  