Bug#37512526 Signal dump code can read out of bounds

Followup fix - remove [[fallthrough]] not supported on
all compilers used for 7.6.

Change-Id: Ifdc5ae688ae2f3d3c64c895ca7a062b1ab0ccc6a

Author: frazerclement

storage/ndb/src/kernel/vm/mt.cpp

@@ -8310,13 +8310,13 @@ FastScheduler::dumpSignalMemory(Uint32 thr_no, FILE* out)
     switch (s->m_noOfSections) {
       case 3:
         signal.m_sectionPtrI[2] = posptr[siglen + 2];
-        [[fallthrough]];
+        /* Fall through */
       case 2:
         signal.m_sectionPtrI[1] = posptr[siglen + 1];
-        [[fallthrough]];
+        /* Fall through */
       case 1:
         signal.m_sectionPtrI[0] = posptr[siglen + 0];
-        [[fallthrough]];
+        /* Fall through */
       case 0:
         break;
       default: