Specifically libgit2 v0.24.3 is incompatible with openssl 1.1.0. Compiling libgit2 with openssl 1.1.0 installed results in the error:

/usr/local/julia/deps/srccache/libgit2-211e117a0590583a720c53172406f34186c543bd/src/openssl_stream.c:217:19: error: storage size of 'git_stream_bio_method' isn't known
 static BIO_METHOD git_stream_bio_method = {
                   ^~~~~~~~~~~~~~~~~~~~~

Problem would be resolved by backporting #18658 which avoids using openssl 1.1.0. Alternatively, we could update the version of libgit2 to v0.25.0-rc1 which is compatible with openssl 1.1.0 but would require some changes to the Julia libgit2 interface.