Yes, this is with Clang. I am working on getting it to compile on Windows with clang-cl, using vcpkg, with success. I have several patches to fix the issues that clang detected, and so I wonder if I should create a Task to discuss them all?

Actually, there's plenty more locations where unistd.h is included unconditionally, all of which should likely embrace in guards like this.

This was apparently discussed before:
https://www.mail-archive.com/ports@openbsd.org/msg105601.html

Also in:

Additionally, poly1305-s390x.S is being compiled despite running/targeting a PC system:

Please also refer to https://github.com/microsoft/vcpkg/discussions/20755 where we discuss on how to approach GnuPG libraries for a native Windows compilation.

Also, and I should maybe have opened with it, the issues vcpkg has with your build system are currently tracked here, while my effort to build gpg-error natively (i.e. without relying on ShiftMediaProject fork) on all platforms is here.

In T5687#151853, @werner wrote:

FWIW, the gnupg installer comes with dll, header and import files. You may use them.

In T5365#151844, @gniibe wrote:

Let me clarify the use case of gpg-error.m4.

gpg-error.m4 is for GnuPG and its friends, where we cannot assume availability of pkg-config. Its capability is limited, and we don't pursue 100% compatibility of pkg-config.

In T5365#144688, @gniibe wrote:

If it is new, it may be the change of this commit rC8e3cd4c4677c: build: Update gpg-error.m4.

I tried following the README instructions, but getting:

I just read https://github.com/gpg/libgpg-error/blob/master/README#L119 and realize this is by design...