In one instance, the kernel build on x86_64 on an Ubuntu box failed with the following error:
[...] fatal error: openssl/opensslv.h: No such file or directory
This is just a case of missing OpenSSL development headers; this is clearly mentioned in the Minimal requirements to compile the kernel document here: https://github.com/torvalds/linux/blob/master/Documentation/process/changes.rst#openssl. Specifically, it mentions that from v4.3 and higher, the openssl development packages are required.
FYI, this Q&A too shows how the installation of the openssl-devel package (or equivalent; for example, on the Raspberry Pi, the libssl-dev package needs to be installed) solves the issue: OpenSSL missing during ./configure. How to fix?, available at https://superuser.com/questions/371901/openssl-missing-during-configure-how-to-fix.
In fact, exactly this error occurred on a vanilla x86_64 Fedora...
