boost_stacktrace_impl_return_nullptr as an exported symbol

[lufriem]

#159 added the 'stacktrace from current exception for MSVC' feature but one (I guess) sideeffect is that I now get an exported symbol 'boost_stacktrace_impl_return_nullptr', which makes MSVS always generate an input library (.lib) for my (non-library, ie EXE) project (its linker just triggers off the __declspec(dllexport) tokens, with no way of suppressing this, see https://developercommunity.visualstudio.com/t/why-is-vs2017-building-an-import-library-for-my-ex/233569#T-N237446-N243028). Due to some (admittedly dodgy) project setup I ran into troubles with this file present (when it did not exist before), which I fixed on my side, but I'm wondering about this export..

I guess there's a reason for having that symbol be exported? I see that using the BOOST_SYMBOL_EXPORT macro I guess I could suppress its creation, but I wouldn't really want to deviate from your default project/configuration defaults..

Sorry for the rambling, I guess my question is, is this expected and something that users just have to deal with?

Thank you