Update V8 to r3431 as required by WebKit r51976.

Change-Id: I567392c3f8c0a0d5201a4249611ac4ccf468cd5b
diff --git a/src/SConscript b/src/SConscript
index 85fd724..3b0df17 100755
--- a/src/SConscript
+++ b/src/SConscript
@@ -159,6 +159,7 @@
     """),
   'simulator:arm': ['arm/simulator-arm.cc'],
   'os:freebsd': ['platform-freebsd.cc', 'platform-posix.cc'],
+  'os:openbsd': ['platform-openbsd.cc', 'platform-posix.cc'],
   'os:linux':   ['platform-linux.cc', 'platform-posix.cc'],
   'os:android': ['platform-linux.cc', 'platform-posix.cc'],
   'os:macos':   ['platform-macos.cc', 'platform-posix.cc'],
@@ -187,6 +188,9 @@
   'os:freebsd': [
     'd8-posix.cc'
   ],
+  'os:openbsd': [
+    'd8-posix.cc'
+  ],
   'os:win32': [
     'd8-windows.cc'
   ],
@@ -264,7 +268,6 @@
     else:
       snapshot_cc = Command('snapshot.cc', [], [])
     snapshot_obj = context.ConfigureObject(env, snapshot_cc, CPPPATH=['.'])
-    libraries_obj = context.ConfigureObject(env, libraries_empty_src, CPPPATH=['.'])
   else:
     snapshot_obj = empty_snapshot_obj
   library_objs = [non_snapshot_files, libraries_obj, snapshot_obj]