Do not set and empty CMAKE_MODULE_PATH when calling cmake.

It seems like this causes problems on some platforms. If the path is empty we can leave it unset anyway.

bin/dunecontrol

@@ -694,8 +694,12 @@ run_default_configure () {
       test -n "$found_libs" && \
           echo "ERROR: your build directory $ABS_BUILDDIR contains libtool built libraries $found_libs, please cleanup" && \
           exit 1
-      echo "$PREPARAMS $CMAKE -DCMAKE_MODULE_PATH=\"$CMAKE_MODULE_PATH\" $CMAKE_PARAMS $CMAKE_FLAGS \"$SRCDIR\""
-      eval $PREPARAMS $CMAKE "-DCMAKE_MODULE_PATH=\"$CMAKE_MODULE_PATH\" $CMAKE_PARAMS $CMAKE_FLAGS \"$SRCDIR\"" || exit 1
+      # Prevent using an empty module path
+      if test -n "$CMAKE_MODULE_PATH"; then
+          _MODULE_PATH="-DCMAKE_MODULE_PATH=\"$CMAKE_MODULE_PATH\""
+      fi
+      echo "$PREPARAMS $CMAKE $_MODULE_PATH $CMAKE_PARAMS $CMAKE_FLAGS \"$SRCDIR\""
+      eval $PREPARAMS $CMAKE "$_MODULE_PATH $CMAKE_PARAMS $CMAKE_FLAGS \"$SRCDIR\"" || exit 1
 }
 
 run_default_make () {