Merge pull request #3148 from gtrensch/fix-issue2993-with-mpi-option

Make -Dwith-mpi respect provided path and ensure "default off" options are turned on only by explicit ON

cmake/ProcessOptions.cmake

@@ -420,7 +420,11 @@ endfunction()
 function( NEST_PROCESS_WITH_MPI )
   # Find MPI
   set( HAVE_MPI OFF PARENT_SCOPE )
-  if ( with-mpi )
+  if ( NOT "${with-mpi}" STREQUAL "OFF" )
+    if ( NOT ${with-mpi} STREQUAL "ON" )
+      # if set, use this prefix
+      set( MPI_ROOT "${with-mpi}" )
+    endif ()
     find_package( MPI REQUIRED )
     if ( MPI_CXX_FOUND )
       set( HAVE_MPI ON PARENT_SCOPE )
@@ -649,7 +653,7 @@ function( NEST_PROCESS_WITH_MPI4PY )
 endfunction ()
 
 function( NEST_PROCESS_USERDOC )
-  if ( with-userdoc )
+  if ( ${with-userdoc} STREQUAL "ON")
     message( STATUS "Configuring user documentation" )
     find_package( Sphinx REQUIRED)
     find_package( Pandoc REQUIRED)
@@ -660,7 +664,7 @@ function( NEST_PROCESS_USERDOC )
 endfunction ()
 
 function( NEST_PROCESS_DEVDOC )
-  if ( with-devdoc )
+  if ( ${with-devdoc} STREQUAL "ON" )
     message( STATUS "Configuring developer documentation" )
     find_package( Doxygen REQUIRED dot )
     set( BUILD_DOXYGEN_DOCS ON PARENT_SCOPE )
@@ -669,7 +673,7 @@ function( NEST_PROCESS_DEVDOC )
 endfunction ()
 
 function( NEST_PROCESS_FULL_LOGGING )
-  if ( with-full-logging )
+  if ( ${with-full-logging} STREQUAL "ON" )
     message( STATUS "Configuring full logging" )
     set( ENABLE_FULL_LOGGING ON PARENT_SCOPE )
   endif ()