ARM64EC: Support directly issuing the NtContinue syscall

This is required for handling SMC with the ResetToConsistentState
arguments as used in Windows, as using the NTDLL exported NtContinue
would wipe out any reserved registers in the ARM64EC ABI.

For Windows the syscall numbers are somewhat stable, and the SVC
instruction can be called directly. Since wine doesn't handle that on
ARM64, hardcode the system call number and manually call into wine
dispatcher. Once wine gains proper syscall thunks, those can be
parsed to get the number and the hardcoding dropped.

Source/Windows/ARM64EC/Module.cpp

@@ -46,9 +46,17 @@ $end_info$
 #include <wine/debug.h>
 
 class ECSyscallHandler;
+
+extern "C" {
 void* X64ReturnInstr; // See Module.S
 extern void* ExitFunctionEC;
 
+// Wine doesn't support issuing direct system calls with SVC, and unlike Windows it doesn't have a 'stable' syscall number for NtContinue
+void* WineSyscallDispatcher;
+// TODO: this really shouldn't be hardcoded, once wine gains proper syscall thunks this can be dropped.
+uint64_t WineNtContinueSyscallId = 0x1a;
+}
+
 struct ThreadCPUArea {
   static constexpr size_t TEBCPUAreaOffset = 0x1788;
   CHPE_V2_CPU_AREA_INFO* Area;
@@ -85,6 +93,9 @@ struct ThreadCPUArea {
   }
 };
 
+
+extern "C" NTSTATUS NtContinueNative(ARM64_NT_CONTEXT* NativeContext, BOOLEAN Alert);
+
 namespace {
 fextl::unique_ptr<FEXCore::Context::Context> CTX;
 fextl::unique_ptr<FEX::DummyHandlers::DummySignalDelegator> SignalDelegator;
@@ -437,7 +448,12 @@ void ProcessInit() {
   X64ReturnInstr = ::VirtualAlloc(nullptr, FEXCore::Utils::FEX_PAGE_SIZE, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
   *reinterpret_cast<uint8_t*>(X64ReturnInstr) = 0xc3;
 
-  Exception::KiUserExceptionDispatcher = GetRedirectedProcAddress(GetModuleHandle("ntdll.dll"), "KiUserExceptionDispatcher");
+  const auto NtDll = GetModuleHandle("ntdll.dll");
+  Exception::KiUserExceptionDispatcher = GetRedirectedProcAddress(NtDll, "KiUserExceptionDispatcher");
+  const auto WineSyscallDispatcherPtr = reinterpret_cast<void**>(GetProcAddress(NtDll, "__wine_syscall_dispatcher"));
+  if (WineSyscallDispatcherPtr) {
+    WineSyscallDispatcher = *WineSyscallDispatcherPtr;
+  }
 }
 
 void ProcessTerm() {}