Make fast tls the default

src/platform-tls.h

 // Copyright 2011 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 12 matching lines @@
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // Platform and architecture specific thread local store functions.
 
 #ifndef V8_PLATFORM_TLS_H_
 #define V8_PLATFORM_TLS_H_
 
-#ifdef V8_FAST_TLS
+#ifndef V8_NO_FAST_TLS
 
 // When fast TLS is requested we include the appropriate
 // implementation header.
 //
 // The implementation header defines V8_FAST_TLS_SUPPORTED if it
 // provides fast TLS support for the current platform and architecture
 // combination.
 
 #if defined(_MSC_VER) && (defined(_WIN32) || defined(_WIN64))
 #include "platform-tls-win32.h"
 #elif defined(__APPLE__)
 #include "platform-tls-mac.h"
 #endif
 
 #endif
 
 #endif  // V8_PLATFORM_TLS_H_