[MacPorts] #57732: legacy-support: fix atcalls properly for Tiger

[MacPorts]

#57732: legacy-support: fix atcalls properly for Tiger
--------------------+----------------------------
 Reporter:  kencu   |      Owner:  (none)
     Type:  defect  |     Status:  new
 Priority:  Normal  |  Milestone:
Component:  ports   |    Version:
 Keywords:  tiger   |       Port:  legacy-support
--------------------+----------------------------
 the atcalls.c source file in macports-legacy-support is written to use
 `__pthread_fchdir`. Tiger does not support this call, so `fchdir` is used
 [https://github.com/macports/macports-legacy-
 support/blob/270e8dfee0e670803ad623da44aee679805dd300/src/atcalls.c#L114
 instead]. `__pthread_fchdir` is available in Leopard and newer.

 Using `fchdir` is not a `thread-safe` approach, however.

 The approach could be re-imagined for Tiger, perhaps using the full
 pathname style used for some calls [https://github.com/macports/macports-
 legacy-
 support/blob/270e8dfee0e670803ad623da44aee679805dd300/src/atcalls.c#L340
 some calls] later in the file.

-- 
Ticket URL: <https://trac.macports.org/ticket/57732>
MacPorts <https://www.macports.org/>
Ports system for macOS