DiskCache: use memory-mapped IO for reads when possible

On Wine, use a unixlib call to get a quality mapping that can track a growing
file.

Source/Windows/UnixLib/FEXUnixLib.cpp

@@ -163,6 +163,19 @@ static NTSTATUS FEXUnixLib_DeleteSHMStatsFileHandler(void* _Args) {
   return STATUS_SUCCESS;
 }
 
+static NTSTATUS FEXUnixLib_MapFileHandler(void* _Args) {
+  auto Args = reinterpret_cast<FEXUnixLib_MapFile*>(_Args);
+  // could find a way to dedupe with DiskCacheFilemapper in FEXInterpreter but it's barely any code
+  // fd was already duped by Wine handle translation
+  Args->Result = mmap(nullptr, Args->MapSize, PROT_READ, MAP_SHARED | MAP_NORESERVE, Args->FD, 0);
+  close(Args->FD);
+  if (Args->Result == (void*)-1) {
+    Args->Result = nullptr;
+    return STATUS_INTERNAL_ERROR;
+  }
+  return STATUS_SUCCESS;
+}
+
 extern "C" const unixlib_entry_t __wine_unix_call_funcs[] = {
   FEXUnixLib_SetHardwareTSOControlHandler,
   FEXUnixLib_SetKernelUnalignedAtomicControlHandler,
@@ -170,6 +183,7 @@ extern "C" const unixlib_entry_t __wine_unix_call_funcs[] = {
   FEXUnixLib_SetVMANameHandler,
   FEXUnixLib_GetSHMStatsVMAHandler,
   FEXUnixLib_DeleteSHMStatsFileHandler,
+  FEXUnixLib_MapFileHandler,
 };
 
 static_assert(sizeof(__wine_unix_call_funcs) / sizeof(__wine_unix_call_funcs[0]) == ToUnderlying(FEXUnixLibFunctions::MAX));