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/pure/concurrency/cpuinfo.nim

@@ -43,6 +43,14 @@ when defined(genode):
   proc affinitySpaceTotal(env: GenodeEnvPtr): cuint {.
     importcpp: "@->cpu().affinity_space().total()".}
 
+when defined(haiku):
+  {.emit: "#include <OS.h>".}
+  type
+    SystemInfo {.importc: "system_info", bycopy.} = object
+      cpuCount {.importc: "cpu_count".}: uint32
+
+  proc getSystemInfo(info: ptr SystemInfo): int32 {.importc: "get_system_info".}
+
 proc countProcessors*(): int {.rtl, extern: "ncpi$1".} =
   ## returns the numer of the processors/cores the machine has.
   ## Returns 0 if it cannot be detected.
@@ -86,6 +94,10 @@ proc countProcessors*(): int {.rtl, extern: "ncpi$1".} =
     result = sysconf(SC_NPROC_ONLN)
   elif defined(genode):
     result = runtimeEnv.affinitySpaceTotal().int
+  elif defined(haiku):
+    var sysinfo: SystemInfo
+    if getSystemInfo(addr sysinfo) == 0:
+      result = sysinfo.cpuCount.int
   else:
     result = sysconf(SC_NPROCESSORS_ONLN)
   if result <= 0: result = 0