Arm64: Removes a vtable indirection in syscalls

We can safely call virtual functions through the JIT with a little bit
of work.

FEX's JIT has quite a few steps before it gets to a syscall handler.

Before this commit:
JIT->static HandleSyscall->SyscallHandler::HandleSyscall->SyscallHandler

After this commit:
JIT->SyscallHandler::HandleSyscall->SyscallHandler

A bit hard to notice this when this interface can spin at 67-million
calls per second though.

FEXCore/Source/Interface/Context/Context.h

@@ -440,6 +440,4 @@ namespace FEXCore::Context {
     fextl::unordered_map<uint64_t, std::tuple<CustomIREntrypointHandler, void *, void *>> CustomIRHandlers;
     FEXCore::CPU::DispatcherConfig DispatcherConfig;
   };
-
-  uint64_t HandleSyscall(FEXCore::HLE::SyscallHandler *Handler, FEXCore::Core::CpuStateFrame *Frame, FEXCore::HLE::SyscallArguments *Args);
 }

FEXCore/Source/Interface/Core/Core.cpp

@@ -1269,12 +1269,6 @@ namespace FEXCore::Context {
     });
   }
 
-  uint64_t HandleSyscall(FEXCore::HLE::SyscallHandler *Handler, FEXCore::Core::CpuStateFrame *Frame, FEXCore::HLE::SyscallArguments *Args) {
-    uint64_t Result{};
-    Result = Handler->HandleSyscall(Frame, Args);
-    return Result;
-  }
-
   IR::AOTIRCacheEntry *ContextImpl::LoadAOTIRCacheEntry(const fextl::string &filename) {
     auto rv = IRCaptureCache.LoadAOTIRCacheEntry(filename);
     return rv;

FEXCore/Source/Interface/Core/JIT/Arm64/JIT.cpp

@@ -29,6 +29,7 @@ desc: Main glue logic of the arm64 splatter backend
 #include <FEXCore/Utils/CompilerDefs.h>
 #include <FEXCore/Utils/EnumUtils.h>
 #include <FEXCore/Utils/Profiler.h>
+#include <FEXCore/HLE/SyscallHandler.h>
 
 #include "Interface/Core/Interpreter/InterpreterOps.h"
 
@@ -574,8 +575,11 @@ Arm64JITCore::Arm64JITCore(FEXCore::Context::ContextImpl *ctx, FEXCore::Core::In
       Common.XCRFunction = PMF.GetConvertedPointer();
     }
 
-    Common.SyscallHandlerObj = reinterpret_cast<uint64_t>(CTX->SyscallHandler);
-    Common.SyscallHandlerFunc = reinterpret_cast<uint64_t>(FEXCore::Context::HandleSyscall);
+    {
+      FEXCore::Utils::MemberFunctionToPointerCast PMF(&FEXCore::HLE::SyscallHandler::HandleSyscall);
+      Common.SyscallHandlerObj = reinterpret_cast<uint64_t>(CTX->SyscallHandler);
+      Common.SyscallHandlerFunc = PMF.GetVTableEntry(CTX->SyscallHandler);
+    }
     Common.ExitFunctionLink = reinterpret_cast<uintptr_t>(&Context::ContextImpl::ThreadExitFunctionLink<Arm64JITCore_ExitFunctionLink>);
 
     // Fill in the fallback handlers