MINOR: ssl: define SSL_CTX_set1_curves_list to itself on BoringSSL

MINOR: ssl: define SSL_CTX_set1_curves_list to itself on BoringSSL

OpenSSL 1.0.2 and onwards define SSL_CTX_set1_curves_list which is both a
function and a macro. OpenSSL 1.0.2 to 1.1.0 define SSL_CTRL_SET_CURVES_LIST
as a macro, which disappeared from 1.1.1. BoringSSL only has that one and
not the former macro but it does have the function. Let's keep the test on
the macro matching the function name by defining the macro to itself when
needed.