Allow build-time selection between ia32 and x86_64 in the GYP/Xcode Mac Chromium build

src/globals.h

 // Copyright 2006-2009 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 41 matching lines @@
 #if CAN_USE_UNALIGNED_ACCESSES
 #define V8_HOST_CAN_READ_UNALIGNED 1
 #endif
 #elif defined(_MIPS_ARCH_MIPS32R2)
 #define V8_HOST_ARCH_MIPS 1
 #define V8_HOST_ARCH_32_BIT 1
 #else
 #error Host architecture was not detected as supported by v8
 #endif
 
+// Target architecture detection. This may be set externally. If not, detect
+// in the same way as the host architecture, that is, target the native
+// environment as presented by the compiler.
+#if !defined(V8_TARGET_ARCH_X64) && !defined(V8_TARGET_ARCH_IA32) && \
+    !defined(V8_TARGET_ARCH_ARM) && !defined(V8_TARGET_ARCH_MIPS)
+#if defined(_M_X64) || defined(__x86_64__)
+#define V8_TARGET_ARCH_X64 1
+#elif defined(_M_IX86) || defined(__i386__)
+#define V8_TARGET_ARCH_IA32 1
+#elif defined(__ARMEL__)
+#define V8_TARGET_ARCH_ARM 1
+#elif defined(_MIPS_ARCH_MIPS32R2)
+#define V8_TARGET_ARCH_MIPS 1
+#else
+#error Target architecture was not detected as supported by v8
+#endif
+#endif
+
 // Check for supported combinations of host and target architectures.
 #if defined(V8_TARGET_ARCH_IA32) && !defined(V8_HOST_ARCH_IA32)
 #error Target architecture ia32 is only supported on ia32 host
 #endif
 #if defined(V8_TARGET_ARCH_X64) && !defined(V8_HOST_ARCH_X64)
 #error Target architecture x64 is only supported on x64 host
 #endif
 #if (defined(V8_TARGET_ARCH_ARM) && \
     !(defined(V8_HOST_ARCH_IA32) || defined(V8_HOST_ARCH_ARM)))
 #error Target architecture arm is only supported on arm and ia32 host
@@ skipping 563 matching lines @@
                   CMOV = 15,   // x86
                   RDTSC = 4,   // x86
                   CPUID = 10,  // x86
                   VFP3 = 1,    // ARM
                   ARMv7 = 2,   // ARM
                   SAHF = 0};   // x86
 
 } }  // namespace v8::internal
 
 #endif  // V8_GLOBALS_H_