OpenBSD doesn't have ucontext.h so don't try and include it
OpenBSD doesn't have ucontext.h so don't try and include it

On OpenBSD we turn off async capabilities due to no ucontext.h.

RT#4379

Reviewed-by: Richard Levitte <5fb523282dd7956571c80524edc2dccfa0bd8234@openssl.org>

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl