Fixed gawk script for git-tar target.

Fixed gawk script for git-tar target.

The previous variant was nice and sleek. But unfortunately, there are
constructs like:

  #if 0
  (... old code ...)
  #else
  (... alternative code for elogind ...)
  #endif // 0

These fragments couldn't be handled by the old code, but can by the
new one.

To make this work, the precompiler macros must be set like shown above.
Apart from that, all lines like:

/// Any doxygen one-line-comments with elogind in it are removed

are removed, too. Please note the three slashes.

And finally, all commented out #include directives are removed as well.