Update V8 to r6101 as required by WebKit r74534

Change-Id: I7f84af8dd732f11898fd644b2c2b1538914cb78d
diff --git a/src/flags.cc b/src/flags.cc
index bbe6bb7..c20f5ee 100644
--- a/src/flags.cc
+++ b/src/flags.cc
@@ -279,7 +279,7 @@
   *value = NULL;
   *is_bool = false;
 
-  if (*arg == '-') {
+  if (arg != NULL && *arg == '-') {
     // find the begin of the flag name
     arg++;  // remove 1st '-'
     if (*arg == '-') {