rts: annotate switch/case with '/* fallthrough */'

Fixes gcc-7.1.0 warnings of form:

  rts/sm/Scav.c:559:9: error:
     error: this statement may fall through [-Werror=implicit-fallthrough=]
             scavenge_fun_srt(info);
             ^~~~~~~~~~~~~~~~~~~~~~

Many of places are indeed unobvious and some are
already annotated by comments.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/rts/RaiseAsync.c b/rts/RaiseAsync.c
index 31cc91587d..e04a875e49 100644
--- a/rts/RaiseAsync.c
+++ b/rts/RaiseAsync.c
@@ -459,6 +459,7 @@ check_target:
         // fall to next
     }
 #endif
+    /* fallthrough */
     case BlockedOnCCall:
         blockedThrowTo(cap,target,msg);
         return THROWTO_BLOCKED;