Do not include headers bearing OpenSSL copyrights by default

[georgthegreat]

We use automatic license analysis and automatic source tracking when we import the code.

At the time license report for libgit2 is overcomplicated.
This PR reorganizes include schema in order to avoid #include-ing openssl_dynamic.h from default build.

It would be nice to add an option disabling openssl_dynamic.c and openssl_legacy.c compilation at all.

This is yet TBD.

[ethomson]

It would be nice to add an option disabling openssl_dynamic.c and openssl_legacy.c compilation at all.

I think that this is the only way that this will work, since GIT_OPENSSL_LEGACY is enabled based on the version of OpenSSL that's in use:

# if (defined(OPENSSL_VERSION_NUMBER) && OPENSSL_VERSION_NUMBER < 0x10100000L) || \
     (defined(LIBRESSL_VERSION_NUMBER) && LIBRESSL_VERSION_NUMBER < 0x20700000L)
#  define GIT_OPENSSL_LEGACY
# endif
#endif

[georgthegreat]

The above code would not work for us, it should be a CMake option, not compile-time CFLAG.

[georgthegreat]

Anyway, this PR does not break anything (I hope so) and solves our problem.

[ethomson]

At the moment, none of the OpenSSL builds in CI are working with this change. 😞

[georgthegreat]

Hmm... I am unable to reproduce this locally.

$ contrib/libgit2@openssl-license$ cmake -DENABLE_WERROR=ON -DBUILD_EXAMPLES=ON -DBUILD_FUZZERS=ON -DUSE_STANDALONE_FUZZERS=ON -G "Ninja" -DUSE_HTTPS=OpenSSL -DREGEX_BACKEND=builtin -DDEPRECATE_HARD=ON -DUSE_LEAK_CHECKER=valgrind -DDEBUG_STRICT_ALLOC=ON -DDEBUG_STRICT_OPEN=ON
$ ninja

I get a binary dynamically linked to openssl:

$ ldd git2
        linux-vdso.so.1 (0x00007ffd3b3fe000)
        libssl.so.1.1 => /usr/lib/x86_64-linux-gnu/libssl.so.1.1 (0x00007ff2a3587000)
        libcrypto.so.1.1 => /usr/lib/x86_64-linux-gnu/libcrypto.so.1.1 (0x00007ff2a32b1000)
        libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007ff2a3295000)
        libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007ff2a3272000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007ff2a3080000)
        libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007ff2a3078000)
        /lib64/ld-linux-x86-64.so.2 (0x00007ff2a37f2000)

Do you have any idea on reproducing this?