BUILD: ssl: use OPENSSL_NO_OCSP to detect OCSP support

Since commit 656c5fa7e859 ("BUILD: ssl: disable OCSP when using
boringssl) the OCSP code is bypassed when OPENSSL_IS_BORINGSSL
is defined. The correct thing to do here is to use OPENSSL_NO_OCSP
instead, which is defined for this exact purpose in
openssl/opensslfeatures.h.

This makes haproxy forward compatible if boringssl ever introduces
full OCSP support with the additional benefit that it links fine
against a OCSP-disabled openssl.

Signed-off-by: Lukas Tribus <luky-37@hotmail.com>