dlopen: log debug message when a library is dlopened

Useful to track what is being used and when

src/basic/dlfcn-util.c

@@ -49,6 +49,8 @@ int dlopen_many_sym_or_warn_sentinel(void **dlp, const char *filename, int log_l
                 return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
                                        "%s is not installed: %s", filename, dlerror());
 
+        log_debug("Loaded '%s' via dlopen()", filename);
+
         va_list ap;
         va_start(ap, log_level);
         r = dlsym_many_or_warnv(dl, log_level, ap);