[MacPorts] #64247: openrct2: builds failing for 10.13 and earlier, with macports-libcxx: cyclic dependency errors

[MacPorts]

#64247: openrct2: builds failing for 10.13 and earlier, with macports-libcxx:
cyclic dependency errors
---------------------+----------------------
 Reporter:  mascguy  |      Owner:  mascguy
     Type:  defect   |     Status:  assigned
 Priority:  Normal   |  Milestone:
Component:  ports    |    Version:
 Keywords:           |       Port:  openrct2
---------------------+----------------------
 In the interest of providing this port to an expanded set of macOS
 releases/users - originally it required 10.15 and later - this port was
 updated to utilize `macports-libcxx`.

 As for the previous 10.15+ requirement, that's related to use of libcxx
 features only present in 10.15 and later. That makes it a perfect
 candidate for `macports-libcxx`, which fills that gap. And thus far, the
 latter works beautifully, based on its use with other ports.

 Of note, it's understood that upstream may be dependent upon newer macOS
 APIs. So it's not yet clear what the floor is, relative to a minimum macOS
 version for this port. (At least without modifications/patches.)

 Nonetheless, at least in local testing, macOS 10.13 does appear to work
 properly: Not just for the build, but at runtime as well. Confirmed by
 running with official Roller Coaster Tycoon 2 game files, purchased from
 GOG.

 However, on our buildbots, builds are failing for 10.13 and earlier. And
 the errors involve potential cyclic dependencies, during header
 inclusion/consumption.

 Here is one example, for 10.13:

 https://build.macports.org/builders/ports-10.13_x86_64-builder/builds/133693/steps
 /install-port/logs/stdio

 {{{
 openrct2/work/OpenRCT2-0.3.5.1/src/openrct2/platform/Platform.macOS.mm
 While building module 'std' imported from
 openrct2/work/OpenRCT2-0.3.5.1/src/openrct2/platform/../Diagnostic.h:12:
 While building module 'Darwin' imported from
 /opt/local/include/libcxx/v1/ctype.h:38:
 In file included from <module-includes>:74:
 In file included from
 /opt/local/libexec/llvm-9.0/lib/clang/9.0.1/include/tgmath.h:21:
 /usr/include/tgmath.h:27:10: fatal error: cyclic dependency in module
 'std': std -> Darwin -> std
 #include <math.h>
          ^
 }}}

 It's possible that this is a relatively simple issue, perhaps related to
 compilation arguments. However, more discussion and investigation is
 needed.

-- 
Ticket URL: <https://trac.macports.org/ticket/64247>
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