x86_64: JNI compiler

Passed all tests from jni_compiler_test and art/test on host with jni_copiler.
Incoming argument spill is enabled, entry_spills refactored. Now each entry spill
contains data type size (4 or 8) and offset which should be used for spill.
Assembler REX support implemented in opcodes used in JNI compiler.
Please note, JNI compiler is not enabled by default yet (see compiler_driver.cc:1875).

Change-Id: I5fd19cca72122b197aec07c3708b1e80c324be44
Signed-off-by: Dmitry Petrochenko <dmitry.petrochenko@intel.com>
diff --git a/compiler/compiled_method.cc b/compiler/compiled_method.cc
index 344f3ef..8e013c1 100644
--- a/compiler/compiled_method.cc
+++ b/compiler/compiled_method.cc
@@ -105,6 +105,7 @@
     case kArm64:
     case kMips:
     case kX86:
+    case kX86_64:
       return 0;
     case kThumb2: {
       // +1 to set the low-order bit so a BLX will switch to Thumb mode
@@ -123,6 +124,7 @@
     case kArm64:
     case kMips:
     case kX86:
+    case kX86_64:
       return code_pointer;
     case kThumb2: {
       uintptr_t address = reinterpret_cast<uintptr_t>(code_pointer);