Fix compilation with GCC 4.8

include/v8config.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 169 matching lines @@
 //
 // Compiler-specific feature detection
 //
 //  V8_HAS___ALIGNOF                    - __alignof(type) operator supported
 //  V8_HAS___ALIGNOF__                  - __alignof__(type) operator supported
 //  V8_HAS_ATTRIBUTE_ALIGNED            - __attribute__((aligned(n))) supported
 //  V8_HAS_ATTRIBUTE_ALWAYS_INLINE      - __attribute__((always_inline))
 //                                        supported
 //  V8_HAS_ATTRIBUTE_DEPRECATED         - __attribute__((deprecated)) supported
 //  V8_HAS_ATTRIBUTE_NOINLINE           - __attribute__((noinline)) supported
+//  V8_HAS_ATTRIBUTE_UNUSED             - __attribute__((unused)) supported
 //  V8_HAS_ATTRIBUTE_VISIBILITY         - __attribute__((visibility)) supported
 //  V8_HAS_ATTRIBUTE_WARN_UNUSED_RESULT - __attribute__((warn_unused_result))
 //                                        supported
 //  V8_HAS_BUILTIN_EXPECT               - __builtin_expect() supported
 //  V8_HAS_DECLSPEC_ALIGN               - __declspec(align(n)) supported
 //  V8_HAS_DECLSPEC_DEPRECATED          - __declspec(deprecated) supported
 //  V8_HAS_DECLSPEC_NOINLINE            - __declspec(noinline) supported
 //  V8_HAS___FINAL                      - __final supported in non-C++11 mode
 //  V8_HAS___FORCEINLINE                - __forceinline supported
 //  V8_HAS_SEALED                       - MSVC style sealed marker supported
 //
 // Note that testing for compilers and/or features must be done using #if
 // not #ifdef. For example, to test for Intel C++ Compiler, use:
 //  #if V8_CC_INTEL
 //   ...
 //  #endif
 
 #if defined(__clang__)
 
 # define V8_CC_CLANG 1
 
 // Clang defines __alignof__ as alias for __alignof
 # define V8_HAS___ALIGNOF 1
 # define V8_HAS___ALIGNOF__ V8_HAS___ALIGNOF
 
 # define V8_HAS_ATTRIBUTE_ALIGNED (__has_attribute(aligned))
 # define V8_HAS_ATTRIBUTE_ALWAYS_INLINE (__has_attribute(always_inline))
 # define V8_HAS_ATTRIBUTE_DEPRECATED (__has_attribute(deprecated))
 # define V8_HAS_ATTRIBUTE_NOINLINE (__has_attribute(noinline))
+# define V8_HAS_ATTRIBUTE_UNUSED (__has_attribute(unused))
 # define V8_HAS_ATTRIBUTE_VISIBILITY (__has_attribute(visibility))
 # define V8_HAS_ATTRIBUTE_WARN_UNUSED_RESULT \
     (__has_attribute(warn_unused_result))
 
 # define V8_HAS_BUILTIN_EXPECT (__has_builtin(__builtin_expect))
 
 # define V8_HAS_CXX11_ALIGNAS (__has_feature(cxx_alignas))
 # define V8_HAS_CXX11_STATIC_ASSERT (__has_feature(cxx_static_assert))
 # define V8_HAS_CXX11_DELETE (__has_feature(cxx_deleted_functions))
 # define V8_HAS_CXX11_FINAL (__has_feature(cxx_override_control))
@@ skipping 11 matching lines @@
 # define V8_HAS___ALIGNOF__ (V8_GNUC_PREREQ(4, 3, 0))
 
 # define V8_HAS_ATTRIBUTE_ALIGNED (V8_GNUC_PREREQ(2, 95, 0))
 // always_inline is available in gcc 4.0 but not very reliable until 4.4.
 // Works around "sorry, unimplemented: inlining failed" build errors with
 // older compilers.
 # define V8_HAS_ATTRIBUTE_ALWAYS_INLINE (V8_GNUC_PREREQ(4, 4, 0))
 # define V8_HAS_ATTRIBUTE_DEPRECATED (V8_GNUC_PREREQ(3, 4, 0))
 # define V8_HAS_ATTRIBUTE_DEPRECATED_MESSAGE (V8_GNUC_PREREQ(4, 5, 0))
 # define V8_HAS_ATTRIBUTE_NOINLINE (V8_GNUC_PREREQ(3, 4, 0))
+# define V8_HAS_ATTRIBUTE_UNUSED (V8_GNUC_PREREQ(2, 95, 0))
 # 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_EXPECT (V8_GNUC_PREREQ(2, 96, 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
@@ skipping 67 matching lines @@
 #elif defined(V8_DEPRECATION_WARNINGS) && V8_HAS_ATTRIBUTE_DEPRECATED
 # define V8_DEPRECATED(message, declarator) \
 declarator __attribute__((deprecated))
 #elif defined(V8_DEPRECATION_WARNINGS) && V8_HAS_DECLSPEC_DEPRECATED
 # define V8_DEPRECATED(message, declarator) __declspec(deprecated) declarator
 #else
 # define V8_DEPRECATED(message, declarator) declarator
 #endif
 
 
+// A macro to mark variables or types as unused, avoiding compiler warnings.
+#if V8_HAS_ATTRIBUTE_UNUSED
+# define V8_UNUSED __attribute__((unused))
+#else
+# define V8_UNUSED
+#endif
+
+
 // Annotate a function indicating the caller must examine the return value.
 // Use like:
 //   int foo() V8_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
 
 
@@ skipping 100 matching lines @@
 # define V8_ALIGNOF(type) __alignof__(type)
 #else
 // Note that alignment of a type within a struct can be less than the
 // alignment of the type stand-alone (because of ancient ABIs), so this
 // should only be used as a last resort.
 namespace v8 { template <typename T> class AlignOfHelper { char c; T t; }; }
 # define V8_ALIGNOF(type) (sizeof(::v8::AlignOfHelper<type>) - sizeof(type))
 #endif
 
 #endif  // V8CONFIG_H_