Clean up the usage of V8_TARGET_ARCH_${arch} and V8_HOST_ARCH_${arch}

src/platform-posix.cc

Index: src/platform-posix.cc
===================================================================
--- src/platform-posix.cc	(revision 15346)
+++ src/platform-posix.cc	(working copy)
@@ -105,7 +105,7 @@
   // CpuFeatures::Probe. We don't care about randomization in this case because
   // the code page is immediately freed.
   if (isolate != NULL) {
-#ifdef V8_TARGET_ARCH_X64
+#if V8_TARGET_ARCH_X64
     uint64_t rnd1 = V8::RandomPrivate(isolate);
     uint64_t rnd2 = V8::RandomPrivate(isolate);
     uint64_t raw_addr = (rnd1 << 32) ^ rnd2;
@@ -321,7 +321,7 @@
 }
 
 
-#if defined(V8_TARGET_ARCH_IA32)
+#if V8_TARGET_ARCH_IA32
 static void MemMoveWrapper(void* dest, const void* src, size_t size) {
   memmove(dest, src, size);
 }
@@ -344,7 +344,7 @@
 
 
 void POSIXPostSetUp() {
-#if defined(V8_TARGET_ARCH_IA32)
+#if V8_TARGET_ARCH_IA32
   OS::MemMoveFunction generated_memmove = CreateMemMoveFunction();
   if (generated_memmove != NULL) {
     memmove_function = generated_memmove;