BUILD: ssl: handle boringssl in openssl version detection

Google's boringssl doesn't have OPENSSL_VERSION_TEXT, SSLeay_version()
or SSLEAY_VERSION, in fact, it doesn't have any real versioning, its
just git-based.

So in case we build against boringssl, we can't access those values.

Instead, we just inform the user that HAProxy was build against
boringssl.

Signed-off-by: Lukas Tribus <luky-37@hotmail.com>
BUILD: ssl: disable OCSP when using boringssl

Google's boringssl doesn't currently support OCSP, so
disable it if detected.

OCSP support may be reintroduced as per:
https://code.google.com/p/chromium/issues/detail?id=398677

In that case we can simply revert this commit.

Signed-off-by: Lukas Tribus <luky-37@hotmail.com>
BUILD: ssl: don't call get_rfc2409_prime when using boringssl

get_rfc2409_prime_1024() and friends are not available in Google's
boringssl, so use the fallback in that case.

Signed-off-by: Lukas Tribus <luky-37@hotmail.com>
MINOR: ssl: don't use boringssl's cipher_list

Google's boringssl has a different cipher_list, we cannot use it as
in OpenSSL. This is due to the "Equal preference cipher groups" feature:

https://boringssl.googlesource.com/boringssl/+/858a88daf27975f67d9f63e18f95645be2886bfb^!/

also see:
https://www.imperialviolet.org/2014/02/27/tlssymmetriccrypto.html

cipher_list is used in haproxy since commit f46cd6e4ec3a ("MEDIUM: ssl:
Add the option to use standardized DH parameters >= 1024 bits") to
check if DHE ciphers are used.

So, if boringssl is used, the patch just assumes that there is some
DHE cipher enabled. This will lead to false positives, but thats better
than compiler warnings and crashes.

This may be replaced one day by properly implementing the the new style
cipher_list, in the meantime this workaround allows to build and use
boringssl.

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