Have TPL MPI produce MPI::all_libs and MPIConfig.cmake (TriBITSPub#299)

This avoids needing to check `if (TARGET <Pkg>::all_libs)` all over the place.

This makes the failing test:

  TriBITS_TribitsOldSimpleExampleApp_STATIC_MPI_USE_DEPRECATED_TARGETS

from the previous commit pass.

Next, we can take out all of these silly checks.

tribits/core/std_tpls/FindTPLMPI.cmake

@@ -50,3 +50,7 @@ if(WIN32 AND TPL_ENABLE_MPI)
   global_set(TPL_MPI_LIBRARIES ${MPI_LIBRARIES})
 endif()
 
+tribits_tpl_find_include_dirs_and_libraries(MPI)
+
+# NOTE: Above, we need to generate the MPI::all_libs target and the
+# MPIConfig.cmake file that will also provide the MPI::all_libs target.