Fix attempt for #177

Author: apolukhin

include/boost/stacktrace/stacktrace.hpp

@@ -37,7 +37,10 @@
 
 extern "C" {
 
-BOOST_SYMBOL_EXPORT inline void* boost_stacktrace_impl_return_nullptr() { return nullptr; }
+#if defined(BOOST_STACKTRACE_LINK) && defined(BOOST_STACKTRACE_DYN_LINK)
+BOOST_SYMBOL_EXPORT
+#endif
+inline void* boost_stacktrace_impl_return_nullptr() { return nullptr; }
 const char* boost_stacktrace_impl_current_exception_stacktrace();
 bool* boost_stacktrace_impl_ref_capture_stacktraces_at_throw();