Silence MSVC warning about unreferenced formal parameter.

Closes #382.

Author: Lastique

src/win32/thread.cpp

@@ -577,10 +577,18 @@ namespace boost
                 } Reason;
             } REASON_CONTEXT, *PREASON_CONTEXT;
             typedef BOOL (WINAPI *setwaitabletimerex_t)(HANDLE, const LARGE_INTEGER *, LONG, PTIMERAPCROUTINE, LPVOID, PREASON_CONTEXT, ULONG);
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable: 4100) // unreferenced formal parameter
+#endif
             static inline BOOL WINAPI SetWaitableTimerEx_emulation(HANDLE hTimer, const LARGE_INTEGER *lpDueTime, LONG lPeriod, PTIMERAPCROUTINE pfnCompletionRoutine, LPVOID lpArgToCompletionRoutine, PREASON_CONTEXT WakeContext, ULONG TolerableDelay)
             {
                 return SetWaitableTimer(hTimer, lpDueTime, lPeriod, pfnCompletionRoutine, lpArgToCompletionRoutine, FALSE);
             }
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
+
 #ifdef _MSC_VER
 #pragma warning(push)
 #pragma warning(disable: 6387) // MSVC sanitiser warns that GetModuleHandleA() might fail