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

[MacPorts]

#57732: legacy-support: fix atcalls properly for Tiger
-----------------------------+----------------------
  Reporter:  kencu           |      Owner:  kencu
      Type:  defect          |     Status:  assigned
  Priority:  Normal          |  Milestone:
 Component:  ports           |    Version:
Resolution:                  |   Keywords:  tiger
      Port:  legacy-support  |
-----------------------------+----------------------
Description changed by kencu:

Old description:

> 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.

New description:

 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 [https://github.com/macports/macports-legacy-
 support/blob/270e8dfee0e670803ad623da44aee679805dd300/src/atcalls.c#L340
 some calls] later in the file.

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Ticket URL: <https://trac.macports.org/ticket/57732#comment:2>
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