filesystem.hpp, add support for Haiku

[Begasus]

No description provided.

[Begasus]

Don't merge yet, need to see if I can find a way to link it to libnetwork on Haiku (for bind and socket).

[jessicah]

https://github.com/gulrak/filesystem/blob/master/cmake/GhcHelper.cmake#L48

Add something like:

if (HAIKU)
  target_link_libraries(${targetName} -lnetwork)
endif()

[jessicah]

You may also need for the second macro, depends which part(s) require libnetwork.

[Begasus]

@jessicah thanks for the tip, following the fix for Solaris I managed to get a full build. :) patch comming in later :)

91e71f7

[jmairboeck]

Just a few style comments.

They apply multiple times, I didn't repeat them.

[Begasus]

Should be OK now, did a clean build on Haiku with this PR as a patch, ran the tests (95% passed), only thing I'm missing is an option to disable Werror, but got a fix for that from Gentoo: https://gitweb.gentoo.org/repo/gentoo.git/tree/dev-cpp/gulrak-filesystem/gulrak-filesystem-1.5.12.ebuild#n22

[Begasus]

Would be nice if this gets merged before a new release: #164 :)

Created a PR at haikuports to have this available on Haiku: haikuports/haikuports#7865

[gulrak]

Looks good to me. If the pipeline goes through, I'll merge it. Thanks for the work!