[MacPorts] #42500: Move cctools-headers, dyld-headers, libunwind-headers

[MacPorts]

#42500: Move cctools-headers, dyld-headers, libunwind-headers
-------------------------+-------------------------------------------------
 Reporter:  mfeiri@…     |      Owner:  jeremyhu@…
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:  2.2.1
 Keywords:               |       Port:  cctools-headers, dyld-headers,
                         |  libunwind-headers, ld64, libcxxabi
-------------------------+-------------------------------------------------
 It turned out that some ports don’t like to find system headers in the
 regular include path (e.g. #39605). For this reason the xnu-headers, libc-
 headers, libm-headers ports have been moved to
 ${prefix}/Developer/SDKs/Darwin${os.major}.sdk (r117043). The other system
 header ports cctools-headers, dyld-headers, libunwind-headers should
 follow suit, but the switch needs to be synchronized with the ports that
 depend on these ports. At this time these are the ld64 and libcxxabi
 ports.

 The process should be straightforward: The *-headers ports install into
 ${prefix}/Developer/SDKs/Darwin${os.major}.sdk and dependent ports include
 a "-isysroot" in the cppflags to find the headers there.

 In the future we might automate this by using the “platform” variable as
 an indicator. The “macosx” ports would require a full Xcode SDK while
 “darwin” platform ports can be compiled with just the open source SDK, if
 it is available. We already have a comparable SDK selection feature for
 universal ports.

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Ticket URL: <https://trac.macports.org/ticket/42500>
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