Use __attribute__((fallthrough)) rather than magic GCC comments.

GCC added an implicit-fallthrough warning a while back, where it
would complain if you had a nontrivial "case:" block that didn't end
with break, return, or something like that.  Clang recently added
the same thing.

GCC, however, would let you annotate a fall-through as intended by
any of various magic "/* fall through */" comments.  Clang, however,
only seems to like "__attribute__((fallthrough))".  Fortunately, GCC
accepts that too.

A previous commit in this branch defined a FALLTHROUGH macro to do
the right thing if GNUC is defined; here we replace all of our "fall
through" comments with uses of that macro.

This is an automated commit, made with the following perl one-liner:

  #!/usr/bin/perl -i -p
  s#/\* *falls? ?thr.*?\*/#FALLTHROUGH;#i;

1 files changed, 1 insertions, 1 deletions

diff --git a/src/feature/rend/rendclient.c b/src/feature/rend/rendclient.c
index 4ca783c7c3..cde954da95 100644
--- a/src/feature/rend/rendclient.c
+++ b/src/feature/rend/rendclient.c
@@ -819,7 +819,7 @@ rend_client_report_intro_point_failure(extend_info_t *failed_intro,
         log_warn(LD_BUG, "Unknown failure type %u. Removing intro point.",
                  failure_type);
         tor_fragile_assert();
-        /* fall through */
+        FALLTHROUGH;
       case INTRO_POINT_FAILURE_GENERIC:
         rend_cache_intro_failure_note(failure_type,
                                       (uint8_t *)failed_intro->identity_digest,