cyassl: define build macros before including ssl.h

cyassl/ssl.h needs the macros from cyassl/options.h, so define them
before including cyassl/ssl.h the first time, which happens in
urldata.h.
This broke the build on Ubuntu Xenial, which comes with WolfSSL 3.4.8
and therefore redefines the symbols from cyassl/options.h instead of
including the header.

Closes https://github.com/curl/curl/pull/1536