Workaround 'inlining failed' build error with older GCC 4.x releases.

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 129 matching lines @@
 # define V8_GNUC_PREREQ(major, minor, patchlevel)                         \
     ((__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) >=   \
      ((major) * 10000 + (minor) * 100 + (patchlevel)))
 
 # define V8_CC_GNU 1
 # if defined(__MINGW32__)
 #  define V8_CC_MINGW 1
 # endif
 
 # define V8_HAS_ATTRIBUTE___ALIGNED__ (V8_GNUC_PREREQ(2, 95, 0))
-# define V8_HAS_ATTRIBUTE_ALWAYS_INLINE (V8_GNUC_PREREQ(4, 0, 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_VISIBILITY (V8_GNUC_PREREQ(4, 3, 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
 // value. Current versions of g++ do not correctly set __cplusplus, so we check
@@ skipping 117 matching lines @@
 # define V8_ALIGNAS(n) alignas(n)
 #elif V8_HAS_ATTRIBUTE___ALIGNED__
 # define V8_ALIGNAS(n) __attribute__((__aligned__(n)))
 #elif V8_HAS_DECLSPEC_ALIGN
 # define V8_ALIGNAS(n) __declspec(align(n))
 #else
 # define V8_ALIGNAS(n) /* NOT SUPPORTED */
 #endif
 
 #endif  // V8CONFIG_H_