GHC_NO_DIRENT_D_TYPE should be defined on Solaris

[lhruska]

Describe the bug
Filesystem fails to compile (filesystem/filesystem.hpp) on Solaris because of missing d_type in dirent structure.

Additional context
Doxygen issue

[gulrak]

I'll look into it.

[phprus]

https://github.com/lukyhruska96/doxygen/commit/f751ce0d514def462798352827515126c45037a5

[albert-github]

The reference: doxygen/doxygen@933c0ec is better as here also the GHC_OS_SOLARIS is set

[gulrak]

I'll decided against another GHC_NO_DIRENT_D_TYPE and instead removed it and implemented compile time detection of the dirent variant. Got the whole test suite to successfully run on a Solaris 10 and hopefully will make a release until tomorrow.
Just need to figure out the GitHub workflow issue with VS2019.

[phprus]

@gulrak
CentOS 8 build is failed.
Solution: migrate from CentOS 8 to CentOS 8 Stream (like this e8a17c1)