Allow for parameter type changes in Qt 5.7 (#69)

In Qt 5.7, a number of endian-swapping function parameters were changed
from uchar to void pointers.

See qtbase commit [5c2ff22](
qt/qtbase@5c2ff22).

src/protobuf/fixnum.cpp

@@ -32,18 +32,28 @@ template<typename Src, typename Dst> inline Dst copyAligned(const Src src)
     return dst;
 }
 
+// In Qt 5.7, these the endian-swapping functions were changed to use void
+// instead of uchar. See Qt commit 5c2ff22ba117f295718c529198ab42ee4646d90c.
+#if (QT_VERSION < QT_VERSION_CHECK(5, 7, 0))
+#define ENDIAN_SWAPPING_PARAM_TYPE const uchar *
+#else
+#define ENDIAN_SWAPPING_PARAM_TYPE const void *
+#endif
+
 // Template specialisation for double (not included in Qt).
-template<> double qFromLittleEndian<double>(const uchar * src)
+template<> double qFromLittleEndian<double>(ENDIAN_SWAPPING_PARAM_TYPE src)
 {
     return copyAligned<quint64, double>(qFromLittleEndian<quint64>(src));
 }
 
 // Template specialisation for float (not included in Qt).
-template<> float qFromLittleEndian<float>(const uchar * src)
+template<> float qFromLittleEndian<float>(ENDIAN_SWAPPING_PARAM_TYPE src)
 {
     return copyAligned<quint32, float>(qFromLittleEndian<quint32>(src));
 }
 
+#undef ENDIAN_SWAPPING_PARAM_TYPE
+
 namespace ProtoBuf {
 
 /// @tparam  Type  May be one of: qint32, quint32, qint64, quint64, float or double.