Gcc 7 fallthrough

Summary:
hopefully the last of the gcc-7 compile errors
Closes https://github.com/facebook/rocksdb/pull/1675

Differential Revision: D4332106

Pulled By: IslamAbdelRahman

fbshipit-source-id: 139448c

util/murmurhash.cc

@@ -46,12 +46,12 @@ uint64_t MurmurHash64A ( const void * key, int len, unsigned int seed )
 
     switch(len & 7)
     {
-    case 7: h ^= ((uint64_t)data2[6]) << 48;
+    case 7: h ^= ((uint64_t)data2[6]) << 48; // fallthrough
-    case 6: h ^= ((uint64_t)data2[5]) << 40;
+    case 6: h ^= ((uint64_t)data2[5]) << 40; // fallthrough
-    case 5: h ^= ((uint64_t)data2[4]) << 32;
+    case 5: h ^= ((uint64_t)data2[4]) << 32; // fallthrough
-    case 4: h ^= ((uint64_t)data2[3]) << 24;
+    case 4: h ^= ((uint64_t)data2[3]) << 24; // fallthrough
-    case 3: h ^= ((uint64_t)data2[2]) << 16;
+    case 3: h ^= ((uint64_t)data2[2]) << 16; // fallthrough
-    case 2: h ^= ((uint64_t)data2[1]) << 8;
+    case 2: h ^= ((uint64_t)data2[1]) << 8; // fallthrough
     case 1: h ^= ((uint64_t)data2[0]);
         h *= m;
     };
@@ -167,8 +167,8 @@ unsigned int MurmurHashNeutral2 ( const void * key, int len, unsigned int seed )
 
     switch(len)
     {
-    case 3: h ^= data[2] << 16;
+    case 3: h ^= data[2] << 16; // fallthrough
-    case 2: h ^= data[1] << 8;
+    case 2: h ^= data[1] << 8; // fallthrough
     case 1: h ^= data[0];
         h *= m;
     };

utilities/document/json_document.cc

@@ -287,7 +287,6 @@ JSONDocument::Type JSONDocument::type() const {
       return JSONDocument::kArray;
 
     case fbson::FbsonType::T_Binary:
-      assert(false);
     default:
       assert(false);
   }