RPM spec improvements

I would like to propose a few improvements to make existing specfiles nicer to read, unfortunately I am not confident in making the changes myself:

1. %define macro can continue with empty parentheses like function in bash
2. Do not highlight leading empty spaces followed by comment. See for example this file https://src.fedoraproject.org/rpms/java-17-openjdk/blob/rawhide/f/java-17-openjdk.spec

I have already opened an MR for adding keywords.