[MacPorts] #63418: mkvtoolnix @ 41.0.0_1 fails to build on 10.11.6 with boost 1.76

[MacPorts]

#63418: mkvtoolnix @ 41.0.0_1 fails to build on 10.11.6 with boost 1.76
----------------------------+------------------------
 Reporter:  sambthompson    |      Owner:  (none)
     Type:  defect          |     Status:  new
 Priority:  Normal          |  Milestone:
Component:  ports           |    Version:  2.7.1
 Keywords:  boost optional  |       Port:  mkvtoolnix
----------------------------+------------------------
 Trying to upgrade from 41.0.0_0 to _1; (seems to be the boost pg change).
 Calls for boost 1.76 and successfully installs it, but the mkvtoolnix
 build fails at:


 {{{
 ... If you want to output boost::optional, include header
 <boost/optional/optional_io.hpp> ...

 }}}

 Log attached. Not sure if related, but based on notes in the portfile
 about being limited to 41.00 due to:

 {{{
     # mkvtoolnix 42.0.0 and later do not build on macOS 10.12 or earlier
     # (at least not with the versions of libc++ included on those systems)
 because:
     # The following features of the C++11/C++14/C++17 standards are not
 supported by /usr/bin/clang++:
     #   * std::optional (C++17)

 }}}

 However, not sure if boost is relying on the underlying std library
 feature?

-- 
Ticket URL: <https://trac.macports.org/ticket/63418>
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