What is particularly bad is that the code uses this header to call the
ssl_cipher_get_evp() function, and this function has different number of
arguments in different openssl versions.

The linked patch replaces the copy of the internal header with a much shorter
header file that only contains the definitions needed to compile the code,
thereby reducing the number of irrelevant lines that could potentially
introduce incompatibilities with the openssl version used. This file has ifdefs
for the parts that are different between the different openssl versions.

Preferably in the long term, the code should be changed to not use openssl
internal functions.