mdbx: add/fix 'fallthrough' for GCC 7.x

Change-Id: I45c57ea910978aaa857086d7794ad92ba0ae7157

src/defs.h

@@ -139,6 +139,14 @@
 #   endif
 #endif /* __deprecated */
 
+#ifndef __fallthrough
+#   if __GNUC_PREREQ(7, 0) || __has_attribute(fallthrough)
+#       define __fallthrough __attribute__((fallthrough))
+#   else
+#       define __fallthrough do {} while(0)
+#   endif
+#endif /* __fallthrough */
+
 #ifndef __packed
 #   if defined(__GNUC__) || __has_attribute(packed)
 #       define __packed __attribute__((packed))

src/mdbx.c

@@ -7067,7 +7067,8 @@ int mdbx_cursor_put(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
             offset *= 4; /* space for 4 more */
             break;
           }
-        /* FALLTHRU: Big enough MDBX_DUPFIXED sub-page */
+          /* FALLTHRU: Big enough MDBX_DUPFIXaED sub-page */
+          __fallthrough;
         case MDBX_CURRENT | MDBX_NODUPDATA:
         case MDBX_CURRENT:
           fp->mp_flags |= P_DIRTY;

src/tools/mdbx_chk.c

@@ -718,6 +718,7 @@ static int check_meta_head(bool steady) {
     assert(false);
     error(" - unexpected internal error (%s)\n",
           steady ? "meta_steady_head" : "meta_weak_head");
+    __fallthrough;
   case 0:
     if (envinfo.mi_meta0_txnid != envinfo.mi_recent_txnid) {
       print(" - meta-%d txn-id mismatch recent-txn-id (%" PRIi64 " != %" PRIi64

src/tools/mdbx_dump.c

@@ -195,6 +195,7 @@ int main(int argc, char *argv[]) {
     case 'l':
       list = 1;
       /*FALLTHROUGH*/;
+      __fallthrough;
     case 'a':
       if (subname)
         usage(prog);

test/config.h

@@ -271,6 +271,7 @@ struct actor_config : public config::actor_config_pod {
     case ac_hill:
       if (!params.test_nops || params.test_nops >= nops)
         return true;
+      __fallthrough;
     default:
       return false;
     }