Fix CheckHookThread calling convention

`CreateThread` expects `lpStartAddress` to be a function with the
signature
DWORD WINAPI ThreadProc(
  _In_ LPVOID lpParameter
);
on Win32 `WINAPI` is `__stdcall`, but `CheckHookThread` previously
had the effective signature
DWORD __cdecl CheckHookThread(LPVOID param);
because the calling convention was unspecified. The cast that was hiding
this error is also removed.

renderdocshim/renderdocshim.cpp

@@ -151,7 +151,7 @@ void CheckHook()
   CloseHandle(datahandle);
 }
 
-DWORD CheckHookThread(LPVOID param)
+DWORD WINAPI CheckHookThread(LPVOID param)
 {
   CheckHook();
 
@@ -170,7 +170,7 @@ BOOL APIENTRY dll_entry(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpRese
 
     // create a thread so that we can perform more complex actions (DllMain must be minimal
     // in size, even this is a bit dodgy).
-    CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)&CheckHookThread, (LPVOID)hModule, 0, NULL);
+    CreateThread(NULL, 0, CheckHookThread, (LPVOID)hModule, 0, NULL);
   }
 
   return TRUE;