Simgear: LARGE_INTEGER is defined in Windows.h

Fixes build issues on Linux.

simgear/io/sg_file.hxx

@@ -88,7 +88,7 @@ public:
     /** @return true of eof conditions exists */
     virtual bool eof() const { return eof_flag; };
 
-    std::string SGFile::computeHash();
+    std::string computeHash();
 
 };
 

simgear/timing/timestamp.cxx

@@ -71,9 +71,12 @@ static clockid_t getClockId()
 }
 
 #endif
+
+#ifdef _WIN32
 static bool qpc_init = false;
 static LARGE_INTEGER s_frequency;
 static BOOL s_use_qpc;
+#endif
 
 void SGTimeStamp::stamp()
 {