Prepend MPI include paths in case of dynamic MPI build (#1585)

* (global) include paths added by cmake could contain unnecessary/undesirable
   MPI library headers for dynamic mpi library (see #1566)
 * in order to have preference for corresponding MPI library headers, prepend mpi
   include path so that those paths are added first.
  See: #1566 (comment)

fixes #1566

src/nrniv/CMakeLists.txt

@@ -322,7 +322,7 @@ if(NRN_ENABLE_MPI)
       list(GET NRN_MPI_LIBNAME_LIST ${val} libname)
 
       add_library(${libname}_lib SHARED ${NRN_NRNMPI_SRC_FILES})
-      target_include_directories(${libname}_lib PUBLIC ${include})
+      target_include_directories(${libname}_lib BEFORE PUBLIC ${include})
       # Note that we do not link here to libmpi. That is dlopen first.
       if(MINGW) # type msmpi only
         add_dependencies(${libname}_lib nrniv_lib)