PageFaultHandler: Determine write flag from ESR on MacOS ARM64

Fixes lockup when running the application from an external drive,
and it is disconnected while running.

Still crashes, but at least it doesn't lock up at 100% CPU.

src/util/page_fault_handler.cpp

@@ -31,6 +31,8 @@
 #endif
 
 #if defined(CPU_ARCH_ARM64)
+static constexpr u64 ARM64_ESR_ISS_DA_WNR = (1u << 6);
+
 [[maybe_unused]] static bool IsStoreInstruction(const void* ptr)
 {
   u32 bits;
@@ -280,9 +282,10 @@ void PageFaultHandler::SignalHandler(int sig, siginfo_t* info, void* ctx)
   void* const exception_pc = reinterpret_cast<void*>(static_cast<ucontext_t*>(ctx)->uc_mcontext->__ss.__rip);
   const bool is_write = (static_cast<ucontext_t*>(ctx)->uc_mcontext->__es.__err & 2) != 0;
 #elif defined(CPU_ARCH_ARM64)
-  void* const exception_address = reinterpret_cast<void*>(static_cast<ucontext_t*>(ctx)->uc_mcontext->__es.__far);
-  void* const exception_pc = reinterpret_cast<void*>(static_cast<ucontext_t*>(ctx)->uc_mcontext->__ss.__pc);
-  const bool is_write = IsStoreInstruction(exception_pc);
+  ucontext_t* const context = static_cast<ucontext_t*>(ctx);
+  void* const exception_address = reinterpret_cast<void*>(context->uc_mcontext->__es.__far);
+  void* const exception_pc = reinterpret_cast<void*>(context->uc_mcontext->__ss.__pc);
+  const bool is_write = (context->uc_mcontext->__es.__esr & ARM64_ESR_ISS_DA_WNR) != 0;
 #else
   void* const exception_address = reinterpret_cast<void*>(info->si_addr);
   void* const exception_pc = nullptr;