basic: fallback to fstatat if entry->d_type is DT_UNKNOWN

basic: fallback to fstatat if entry->d_type is DT_UNKNOWN

* tests-functions: improve FSTYPE-support

make clean setup FSTYPE=reiserfs is working fine now :)

* basic: fallback to fstatat if entry->d_type is DT_UNKNOWN

Fixes localectl on reiserfs:

-bash-4.3# mkdir -p /usr/lib/locale
-bash-4.3# stat -f /usr/lib/locale/
  File: "/usr/lib/locale/"
    ID: bdb0322715b5366e Namelen: 255     Type: reiserfs
Block size: 4096
Blocks: Total: 99835      Free: 60262      Available: 60262
Inodes: Total: 0          Free: 0
-bash-4.3# mkdir /usr/lib/locale/HeyHo
-bash-4.3# localectl list-locales --no-pager

-bash-4.3# mount -t tmpfs tmpfs /usr/lib/locale
-bash-4.3# mkdir /usr/lib/locale/HeyHo
-bash-4.3# localectl list-locales --no-pager
HeyHo