clang-format: update c/cc coding style

Update all cc code using .clang-format; please do so as well for future PRs
etc.; emacs has a handy 'clang-format' mode to make this automatic.

For comparing old changes with git blame, we can disregard this one using
--ignore-rev

(see https://www.moxio.com/blog/43/ignoring-bulk-change-commits-with-git-blame )

lib/mu-xapian.hh

@@ -17,7 +17,6 @@
 **  02110-1301, USA.
 */
 
-
 #ifndef __XAPIAN_HH__
 #define __XAPIAN_HH__
 
@@ -33,7 +32,7 @@ namespace Mu {
  *
  * @return a Xapian query object
  */
-Xapian::Query xapian_query (const Mu::Tree& tree);
+Xapian::Query xapian_query(const Mu::Tree& tree);
 
 } // namespace Mu