Reduce the source widget page-step by one line.

Frequently, the bottom-most visible line is only half-visible, so when I
page down, I don't want the bottom half of that line appearing on top -- I
want to see the entire line.
Stop creating an empty $$LIBEXEC_DIR/sw-libstdcxx-path file.

If there is no libstdc++.so.6 in the CLANG_DIR, then the
$$LIBEXEC_DIR/sw-libstdcxx-path file should be non-existent, not empty.
The linux-wrapper.sh script checks for the existence of this file.