Fix host architecture for 64bit.

Also, hack x86 assembler for use as a x86-64 trampoline compiler's assembler.
Implement missing x86-64 quick resolution trampoline.
Add x86-64 to the quick elf writer.

Change-Id: I08216c67014a83492ada12898ab8000218ba7bb4
diff --git a/compiler/compiled_method.cc b/compiler/compiled_method.cc
index d884bc0..17c2e94 100644
--- a/compiler/compiled_method.cc
+++ b/compiler/compiled_method.cc
@@ -88,7 +88,8 @@
       return RoundUp(offset, kArmAlignment);
     case kMips:
       return RoundUp(offset, kMipsAlignment);
-    case kX86:
+    case kX86:  // Fall-through.
+    case kX86_64:
       return RoundUp(offset, kX86Alignment);
     default:
       LOG(FATAL) << "Unknown InstructionSet: " << instruction_set;