Use C++11 / gnu++11, not 0x

include/v8config.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8CONFIG_H_
 #define V8CONFIG_H_
 
 // clang-format off
 
 // Platform headers for feature detection below.
@@ skipping 248 matching lines @@
 # define V8_HAS_ATTRIBUTE_VISIBILITY (V8_GNUC_PREREQ(4, 3, 0))
 # define V8_HAS_ATTRIBUTE_WARN_UNUSED_RESULT \
     (!V8_CC_INTEL && V8_GNUC_PREREQ(4, 1, 0))
 
 # define V8_HAS_BUILTIN_CLZ (V8_GNUC_PREREQ(3, 4, 0))
 # define V8_HAS_BUILTIN_CTZ (V8_GNUC_PREREQ(3, 4, 0))
 # define V8_HAS_BUILTIN_EXPECT (V8_GNUC_PREREQ(2, 96, 0))
 # define V8_HAS_BUILTIN_FRAME_ADDRESS (V8_GNUC_PREREQ(2, 96, 0))
 # define V8_HAS_BUILTIN_POPCOUNT (V8_GNUC_PREREQ(3, 4, 0))
 
-// g++ requires -std=c++0x or -std=gnu++0x to support C++11 functionality
-// without warnings (functionality used by the macros below).  These modes
-// are detectable by checking whether __GXX_EXPERIMENTAL_CXX0X__ is defined or,
-// more standardly, by checking whether __cplusplus has a C++11 or greater
-// value. Current versions of g++ do not correctly set __cplusplus, so we check
-// both for forward compatibility.
-# if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
+# if __cplusplus >= 201103L
 #  define V8_HAS_CXX11_ALIGNAS (V8_GNUC_PREREQ(4, 8, 0))
 #  define V8_HAS_CXX11_ALIGNOF (V8_GNUC_PREREQ(4, 8, 0))
 # endif
 #endif
 
 #if defined(_MSC_VER)
 # define V8_CC_MSVC 1
 # define V8_HAS___ALIGNOF 1
 
 # define V8_HAS_DECLSPEC_ALIGN 1
@@ skipping 143 matching lines @@
 //   int foo() WARN_UNUSED_RESULT;
 #if V8_HAS_ATTRIBUTE_WARN_UNUSED_RESULT
 #define V8_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
 #else
 #define V8_WARN_UNUSED_RESULT /* NOT SUPPORTED */
 #endif
 
 // clang-format on
 
 #endif  // V8CONFIG_H_