Haiku support for Nim (#8542)

* posix_other: Haiku now has spawn.h

This is added per https://dev.haiku-os.org/ticket/13446

* posix_other: Add Haiku specific Dirent members

* cpuinfo: Add an implementation for Haiku

* distros: Add basic Haiku support

* encodings: update Haiku support

* fenv, math: Haiku now provides libm

* times: Add Haiku struct members

* ansi_c, osalloc: Add Haiku constants

* threads: Add Haiku support

* testament: Haiku uses LIBRARY_PATH

* nim.cfg: Update Haiku support

libnetwork should only be linked if network functions are used

* threads: Haiku does not support -pthread switch

* tworkingdir: Haiku's env is in /bin

* posix_other: add SIGKILLTHR for Haiku

* sockets: link with libnetwork on Haiku

* coro: correct ucontext.h location

http://pubs.opengroup.org/onlinepubs/009696699/basedefs/ucontext.h.html

* coro: ucontext backend is not available on Haiku

Haiku doesn't provide the <ucontext.h> header, as it was removed from POSIX

* coro: fix setjmp backend

The compiler does not allow statements after a noreturn function

* nativesockets: Haiku doesn't support AI_V4MAPPED

* system: hostOS can contains "haiku"

* os: add support for Haiku's packagefs

packagefs is read-only, but there are writable holes to the underlying
file system as well

* os: update constant for Haiku

lib/posix/posix_other.nim

@@ -10,7 +10,7 @@
 {.deadCodeElim: on.}  # dce option deprecated
 
 const
-  hasSpawnH = not defined(haiku) # should exist for every Posix system nowadays
+  hasSpawnH = true # should exist for every Posix system nowadays
   hasAioH = defined(linux)
 
 when defined(linux) and not defined(android):
@@ -43,6 +43,9 @@ type
 
   Dirent* {.importc: "struct dirent",
              header: "<dirent.h>", final, pure.} = object ## dirent_t struct
+    when defined(haiku):
+      d_dev*: Dev ## Device (not POSIX)
+      d_pdev*: Dev ## Parent device (only for queries) (not POSIX)
     d_ino*: Ino  ## File serial number.
     when defined(dragonfly):
       # DragonflyBSD doesn't have `d_reclen` field.
@@ -54,6 +57,9 @@ type
                     ## (not POSIX)
       when defined(linux) or defined(openbsd):
         d_off*: Off  ## Not an offset. Value that ``telldir()`` would return.
+    elif defined(haiku):
+      d_pino*: Ino ## Parent inode (only for queries) (not POSIX)
+      d_reclen*: cushort ## Length of this record. (not POSIX)
 
     d_name*: array[0..255, char] ## Name of entry.
 
@@ -599,6 +605,10 @@ else:
     MSG_NOSIGNAL* {.importc, header: "<sys/socket.h>".}: cint
       ## No SIGPIPE generated when an attempt to send is made on a stream-oriented socket that is no longer connected.
 
+when defined(haiku):
+  const
+    SIGKILLTHR* = 21 ## BeOS specific: Kill just the thread, not team
+
 when hasSpawnH:
   when defined(linux):
     # better be safe than sorry; Linux has this flag, macosx doesn't, don't