add a few missing (void) to please clang

[omar-polo]

Spotted building with clang 16. The warnings are:

./options.h:20:49: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
LSEC_API lsec_ssl_option_t* lsec_get_ssl_options();
                                                ^
                                                 void

etc.

With this applied, it builds without warnings on OpenBSD-CURRENT w/ clang 16.0.6