Unresolved external symbols: mqtt::message::DFLT_QOS and mqtt::message::DFLT_RETAINED in x86-windows build (VS2022, C++14)

[Alohaq]

VS2022, C++14, using vcpkg for package management, configured as x86-windows. The following compilation issues occur:

Unresolved external symbol "public: static int const mqtt::message::DFLT_QOS" (?DFLT_QOS@message@mqtt@@2HB).
Unresolved external symbol "public: static bool const mqtt::message::DFLT_RETAINED" (?DFLT_RETAINED@message@mqtt@@2_NB).

[fpagliughi]

This keeps popping up and appears to be related to how different compilers (particularly MSVC) handle differences in linkage between C++11 and C++17 (and beyond) components. The new version, v1.5, which will be out soon, moves this library to C++17, and hopefully fixes the problem.