qt-faststart: Undefine fseeko/ftello before defining them

This avoids a number of redefinition warnings on MinGW64.

tools/qt-faststart.c

@@ -30,10 +30,14 @@
 #include <string.h>
 
 #ifdef __MINGW32__
+#undef fseeko
 #define fseeko(x, y, z) fseeko64(x, y, z)
+#undef ftello
 #define ftello(x)       ftello64(x)
 #elif defined(_WIN32)
+#undef fseeko
 #define fseeko(x, y, z) _fseeki64(x, y, z)
+#undef ftello
 #define ftello(x)       _ftelli64(x)
 #endif