Fix build for non-linux architectures but still glibc-based

[mapreri]

Exampls of these are gnu/kfreebsd and gnu/hurd, both available as
unofficial Debian ports.

They don't define __linux__ (as they are non-linux…) but still define
__GLIBC__, so check on that.

[alalek]

Does this really robust solution? For example, MinGW uses GLIBC/GLIBCXX internally, but we don't want to call "sysconf" in this case.

[mapreri]

uhh, no idea really. I'm not a windows dev at all, and know next to nothing about it.
But I see a windows build on your CI, doesn't that cover what you just said?

[alalek]

We don't have MinGW builds actually (we test more native way: MSVS)

[vpisarev]

@mapreri, thank you for the patch! FreeBSD flavors seem to be handled already. For HURD you can use more specific GNU macro, which will be consistent with other OS'es, such as Linux (we use linux), Mac (we use APPLE) etc.

[mapreri]

@vpisarev

FreeBSD flavors seem to be handled already

Note that here I'm talking about kFreeBSD, which does not define __FreeBSD__ (besides, FreeBSD doesn't use GLIBC). In kFreeBSD __FreeBSD_kernel__ is defined though.

For HURD you can use more specific __GNU__ macro

Yes, __GNU__ would work great for Hurd, but wouldn't cover our (admittedly weird) kFreeBSD case.

[vpisarev]

@mapreri, ok, I see. @mshabunin checked this with MinGW and seems to work well. Let's put it in 👍

[mapreri]

Great, thank you!

If it turns out this breaks some other arch/system combination, feel free to ping me to see about solving it differently :)