openssl: enable PKCS12 support for !BoringSSL

[bagder]

Enable PKCS12 for all non-boringssl builds without relying on configure
or cmake checks.

Bug: https://curl.haxx.se/mail/lib-2017-10/0007.html
Reported-by: Christian Schmitz

[bagder]

No feedback on this take but I merged anyway as I believe this is the right way forward.

[gvanem]

What about the case with multiple SSL backends; both -DUSE_OPENSSL (meaning true OpenSSL) and
-DOPENSSL_IS_BORINGSSL?

Is it possible to detect that at compile time? No #error don't do that! for that in the code now AFAICS..

[jay]

What about the case with multiple SSL backends; both -DUSE_OPENSSL (meaning true OpenSSL) and
-DOPENSSL_IS_BORINGSSL?

I don't think it's possible to use both of those at the same time. edit: I mean you either use openssl or boringssl. USE_OPENSSL should be defined in either case

[gvanem]

I know; I got the error for a missing <pkcs12.h> in BoringSSL. Hence the question.

[jay]

I'm lost. If you are building with BoringSSL then the pkcs stuff should not be included. In other words -DUSE_OPENSSL -DOPENSSL_IS_BORINGSSL then no pkcs