ENH: make FOAM_EXT_LIBBIN optional in the configuration files

- useful for builds that don't use the ThirdParty directory at all

etc/config.csh/mpi

@@ -32,7 +32,7 @@
 #     wmake/rules/General/mplibUSERMPI file and managing all settings
 #
 #------------------------------------------------------------------------------
-unsetenv MPI_ARCH_PATH MPI_HOME FOAM_MPI_LIBBIN
+unsetenv MPI_ARCH_PATH MPI_HOME
 
 switch ("$WM_MPLIB")
 case SYSTEMOPENMPI:
@@ -249,16 +249,17 @@ endsw
 
 
 # Add (non-dummy) MPI implementation
-# Dummy MPI already added to LD_LIBRARY_PATH and has no external libraries
+# - dummy MPI already added to LD_LIBRARY_PATH and has no external libraries
 if ( "$FOAM_MPI" != dummy ) then
-    _foamAddLib ${FOAM_LIBBIN}/${FOAM_MPI}:${FOAM_EXT_LIBBIN}/${FOAM_MPI}
+    if ( $?FOAM_EXT_LIBBIN ) then   # External libraries (allowed to be unset)
+        _foamAddLib ${FOAM_EXT_LIBBIN}/${FOAM_MPI}
+    endif
+    _foamAddLib ${FOAM_LIBBIN}/${FOAM_MPI}
 endif
 
 
-# Set the minimum MPI buffer size (used by all platforms except SGI MPI)
-# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+# Minimum MPI buffer size (used by all except SGI MPI)
 if ( ! $?minBufferSize ) set minBufferSize=20000000
-
 if ( $?MPI_BUFFER_SIZE ) then
     if ( $MPI_BUFFER_SIZE < $minBufferSize ) then
         setenv MPI_BUFFER_SIZE $minBufferSize

etc/config.csh/settings

@@ -197,8 +197,11 @@ endif
 unset siteDir
 
 _foamAddPath ${FOAM_USER_APPBIN}:${FOAM_SITE_APPBIN}:${FOAM_APPBIN}
-# Make sure to pick up dummy versions of external libraries last
-_foamAddLib  ${FOAM_USER_LIBBIN}:${FOAM_SITE_LIBBIN}:${FOAM_LIBBIN}:${FOAM_EXT_LIBBIN}:${FOAM_LIBBIN}/dummy
+_foamAddLib  $FOAM_LIBBIN/dummy     # Dummy versions of external libraries last
+if ( $?FOAM_EXT_LIBBIN ) then       # External libraries (allowed to be unset)
+    _foamAddLib $FOAM_EXT_LIBBIN
+endif
+_foamAddLib  ${FOAM_USER_LIBBIN}:${FOAM_SITE_LIBBIN}:${FOAM_LIBBIN}
 
 #------------------------------------------------------------------------------
 

etc/config.sh/mpi

@@ -32,7 +32,7 @@
 #     wmake/rules/General/mplibUSERMPI file and managing all settings
 #
 #------------------------------------------------------------------------------
-unset MPI_ARCH_PATH MPI_HOME FOAM_MPI_LIBBIN
+unset MPI_ARCH_PATH MPI_HOME
 
 case "$WM_MPLIB" in
 SYSTEMOPENMPI)
@@ -264,17 +264,19 @@ INTELMPI)
 esac
 
 # Add (non-dummy) MPI implementation
-# Dummy MPI already added to LD_LIBRARY_PATH and has no external libraries
+# - dummy MPI already added to LD_LIBRARY_PATH and has no external libraries
 if [ "$FOAM_MPI" != dummy ] && type _foamAddLib > /dev/null 2>&1
 then
-    _foamAddLib $FOAM_LIBBIN/$FOAM_MPI:$FOAM_EXT_LIBBIN/$FOAM_MPI
+    if [ -n "$FOAM_EXT_LIBBIN" ]    # External libraries (allowed to be unset)
+    then
+        _foamAddLib $FOAM_EXT_LIBBIN/$FOAM_MPI
+    fi
+    _foamAddLib $FOAM_LIBBIN/$FOAM_MPI
 fi
 
 
-# Set the minimum MPI buffer size (used by all platforms except SGI MPI)
-# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+# Minimum MPI buffer size (used by all except SGI MPI)
 : ${minBufferSize:=20000000}
-
 if [ "${MPI_BUFFER_SIZE:=$minBufferSize}" -lt $minBufferSize ]
 then
     MPI_BUFFER_SIZE=$minBufferSize

etc/config.sh/settings

@@ -198,8 +198,12 @@ fi
 unset siteDir
 
 _foamAddPath $FOAM_USER_APPBIN:$FOAM_SITE_APPBIN:$FOAM_APPBIN
-# Make sure to pick up dummy versions of external libraries last
-_foamAddLib  $FOAM_USER_LIBBIN:$FOAM_SITE_LIBBIN:$FOAM_LIBBIN:$FOAM_EXT_LIBBIN:$FOAM_LIBBIN/dummy
+_foamAddLib  $FOAM_LIBBIN/dummy     # Dummy versions of external libraries last
+if [ -n "$FOAM_EXT_LIBBIN" ]        # External libraries (allowed to be unset)
+then
+    _foamAddLib $FOAM_EXT_LIBBIN
+fi
+_foamAddLib  $FOAM_USER_LIBBIN:$FOAM_SITE_LIBBIN:$FOAM_LIBBIN
 
 #------------------------------------------------------------------------------