[MacPorts] #69867: legacy-support headers should work with later SDK versions

[MacPorts]

#69867: legacy-support headers should work with later SDK versions
-----------------------------+-----------------------
  Reporter:  fhgwright       |      Owner:  fhgwright
      Type:  defect          |     Status:  closed
  Priority:  Low             |  Milestone:
 Component:  ports           |    Version:  2.9.3
Resolution:  fixed           |   Keywords:
      Port:  legacy-support  |
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Comment (by fhgwright):

 In [changeset:"bd4acde3ef5abb100c78e3ffe9df7c73a01f63e3/macports-ports"
 bd4acde3ef5abb100c78e3ffe9df7c73a01f63e3/macports-ports] (master):
 {{{
 #!ConfigurableCommitTicketReference repository="macports-ports"
 revision="bd4acde3ef5abb100c78e3ffe9df7c73a01f63e3"
 legacy-support-devel: Update to latest master

 - Adds appropriate __DARWIN_C_LEVEL conditionals, as in SDK headers.
   Re: https://trac.macports.org/ticket/69688

 - Completes rework for "mismatched" SDK compatibility.
   Re: https://trac.macports.org/ticket/69867

 - Makes clockid_t an enum, matching SDK behavior.

 - Makes mildly invasive support for "earlier" SDKs a non-default
   option.

 TESTED:
 Tested both normal and -devel versions on 10.4-10.5 ppc, 10.5-10.6 ppc
 (i386 Rosetta), 10.4-10.6 i386, 10.4-12.x x86_64, and 11.x-14.x arm64.
 Builds on all tested platforms except 10.4 ppc +universal.
 Passes all tests in all buildable cases.
 }}}

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Ticket URL: <https://trac.macports.org/ticket/69867#comment:20>
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