command_util: Avoid empty output lines.

Additional empty output lines do not matter for the generated C code or
the function declarations in the header files.  However, a subsequent
commit changes command_util.sh to  generate a preprocessor macro for
the header file, and there we can not afford empty lines unless they
end with a backslash to continue the line.

This patch makes sure that no superfluous newlines are printed in
the output.