deps: cherry-pick 70c4340 from upstream V8

Original commit message:

    [log][api] Fix GCC 4.9 build failure

    GCC 4.9 used on some Node.js CI machines complains when the control
    reaches the end of a non-void function and no return is encountered.

    R=bmeurer@google.com, ofrobots@google.com, yangguo@google.com

    Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
    Change-Id: I5af0192cb187eccbf34dbb60ff3ac2e4774af803
    Reviewed-on: https://chromium-review.googlesource.com/1105619
    Reviewed-by: Yang Guo <yangguo@chromium.org>
    Commit-Queue: Yang Guo <yangguo@chromium.org>
    Cr-Commit-Position: refs/heads/master@{nodejs#53861}

Refs: v8/v8@70c4340

PR-URL: nodejs#21126
Refs: v8/v8@aa6ce3e
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

common.gypi

@@ -28,7 +28,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.5',
+    'v8_embedder_string': '-node.6',
 
     # Enable disassembler for `--print-code` v8 options
     'v8_enable_disassembler': 1,

deps/v8/src/api.cc

@@ -10148,6 +10148,10 @@ const char* CodeEvent::GetCodeEventTypeName(CodeEventType code_event_type) {
       CODE_EVENTS_LIST(V)
 #undef V
   }
+  // The execution should never pass here
+  UNREACHABLE();
+  // NOTE(mmarchini): Workaround to fix a compiler failure on GCC 4.9
+  return "Unknown";
 }
 
 CodeEventHandler::CodeEventHandler(Isolate* isolate) {

deps/v8/src/log.cc

@@ -59,6 +59,10 @@ static v8::CodeEventType GetCodeEventTypeForTag(
       TAGS_LIST(V)
 #undef V
   }
+  // The execution should never pass here
+  UNREACHABLE();
+  // NOTE(mmarchini): Workaround to fix a compiler failure on GCC 4.9
+  return v8::CodeEventType::kUnknownType;
 }
 #define CALL_CODE_EVENT_HANDLER(Call) \
   if (listener_) {                    \