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/core/or/circuituse.c b/src/core/or/circuituse.c
index 000a7c36da..7273be3510 100644
--- a/src/core/or/circuituse.c
+++ b/src/core/or/circuituse.c
@@ -780,7 +780,7 @@ circuit_expire_building(void)
             TO_ORIGIN_CIRCUIT(victim)->build_state->pending_final_cpath ==
             NULL)
           break;
-        /* fallthrough! */
+        FALLTHROUGH;
       case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
       case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
         /* If we have reached this line, we want to spare the circ for now. */