tests: Avoid type punning doubles to uint64_t

When GCC is run with -fstrict-aliasing it complains about type punning
from a double to a uint64_t. The recommended way to avoid this problem
is to use memcpy. The compiler ought to be clever enough to realise that
it doesn't actually need to do any copying.

(This is a deliberately different choice to the implementation in
MessageIStream::read in the hope that it means that we're testing the
implementation correctly.)

tests/dbus_messageistream_unittest.cpp

@@ -74,7 +74,9 @@ namespace test {
         double value = 0.75483;
         MessageIStream leStream((const uint8_t*)&value, sizeof(double), false);
 
-        uint64_t swapped_value = __bswap_64(*reinterpret_cast<uint64_t*>(&value));
+        uint64_t swapped_value;
+        memcpy(&swapped_value, &value, sizeof(value));
+        swapped_value = __bswap_64(swapped_value);
         MessageIStream beStream((const uint8_t*)&swapped_value, sizeof(double),
             true);
 

tests/dbus_type_dictentry_unittest.cpp

@@ -103,7 +103,8 @@ namespace test {
         while (data.size() % 8 != 0)
             data.push_back('\0');
 
-        uint64_t value1 = *reinterpret_cast<const uint64_t*>(&value.first);
+        uint64_t value1;
+        memcpy(&value1, &value.first, sizeof(value1));
         if (byteOrder != __BYTE_ORDER) {
             value1 = __bswap_64(value1);
         }

tests/dbus_type_double_unittest.cpp

@@ -9,7 +9,8 @@ namespace test {
     void TestUnmarshallFromMessageIStream(Type::Double& dbusType, double value,
         unsigned byteOrder)
     {
-        uint64_t u = *reinterpret_cast<uint64_t*>(&value);
+        uint64_t u;
+        memcpy(&u, &value, sizeof(u));
 
         // __FLOAT_WORD_ORDER__ is the same as __BYTE_ORDER__ on almost
         // everything in the world. We only swap or not so we couldn't