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This is quite a substantial change because of the changes to ENGINEs in
BoringSSL.

For the most part, #ifs are used to allow the code to work with either
OpenSSL or BoringSSL. However, in several places, support for things
that BoringSSL is dropping have been removed, even when OpenSSL is used.
This includes DSA keys and tests for the ENGINE bits that are going away
because it's unclear how to skip compiling those tests.

Change-Id: I941a5ed232391f84b45e070c19d2ffb7ad162b7b