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 )

guile/mu-guile-message.hh

@@ -27,6 +27,8 @@
  *
  * @return
  */
-extern "C" { void* mu_guile_message_init (void *data);}
+extern "C" {
+void* mu_guile_message_init(void* data);
+}
 
 #endif /*MU_GUILE_MESSAGE_HH__*/