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/elf_writer_quick.cc b/compiler/elf_writer_quick.cc
index 4b823ef..a6daa5d 100644
--- a/compiler/elf_writer_quick.cc
+++ b/compiler/elf_writer_quick.cc
@@ -377,6 +377,11 @@
       elf_header.e_flags = 0;
       break;
     }
+    case kX86_64: {
+      elf_header.e_machine = EM_X86_64;
+      elf_header.e_flags = 0;
+      break;
+    }
     case kMips: {
       elf_header.e_machine = EM_MIPS;
       elf_header.e_flags = (EF_MIPS_NOREORDER |