Add implicit checks for x86_64 architecture.

This combines the x86 and x86_64 fault handlers into one.  It also
merges in the change to the entrypoints for X86_64.

Replaces generic instruction length calculator with one that only
works with the specific instructions we use.

Bug: 16256184

Change-Id: I1e8ab5ad43f46060de9597615b423c89a836035c
Signed-off-by: Chao-ying Fu <chao-ying.fu@intel.com>
diff --git a/runtime/arch/arm64/fault_handler_arm64.cc b/runtime/arch/arm64/fault_handler_arm64.cc
index dc82cc2..3a7e689 100644
--- a/runtime/arch/arm64/fault_handler_arm64.cc
+++ b/runtime/arch/arm64/fault_handler_arm64.cc
@@ -37,7 +37,7 @@
 
 namespace art {
 
-void FaultManager::GetMethodAndReturnPCAndSP(siginfo_t* siginfo, void* context,
+void FaultManager::GetMethodAndReturnPcAndSp(siginfo_t* siginfo, void* context,
                                              mirror::ArtMethod** out_method,
                                              uintptr_t* out_return_pc, uintptr_t* out_sp) {
   struct ucontext *uc = reinterpret_cast<struct ucontext *>(context);