[MacPorts] #64278: ixion @0.17.0: fatal error: 'variant' file not found

[MacPorts]

#64278: ixion @0.17.0: fatal error: 'variant' file not found
------------------------+----------------------
 Reporter:  ryandesign  |      Owner:  Tatsh
     Type:  defect      |     Status:  assigned
 Priority:  Normal      |  Milestone:
Component:  ports       |    Version:  2.7.1
 Keywords:              |       Port:  ixion
------------------------+----------------------
 https://build.macports.org/builders/ports-10.13_x86_64-builder/builds/134192/steps
 /install-port/logs/stdio
 {{{
   CXX      address.lo
   CXX      address_iterator.lo
   CXX      calc_status.lo
   CXX      cell.lo
   CXX      cell_access.lo
   CXX      compute_engine.lo
   CXX      concrete_formula_tokens.lo
   CXX      config.lo
   CXX      debug.lo
   CXX      dirty_cell_tracker.lo
 In file included from cell.cpp:16:
 ../../include/ixion/matrix.hpp:16:10: fatal error: 'variant' file not
 found
 #include <variant>
          ^~~~~~~~~
 In file included from cell_access.cpp:10:
 ../../include/ixion/model_context.hpp:16:10: fatal error: 'variant' file
 not found
 #include <variant>
          ^~~~~~~~~
 1 error generated.
 make[3]: *** [cell.lo] Error 1
 make[3]: *** Waiting for unfinished jobs....
 }}}

 Perhaps it requires a particular recent C++ standard which could be
 indicated with `compiler.cxx_standard`.

 Also, silent rules should be disabled.

-- 
Ticket URL: <https://trac.macports.org/ticket/64278>
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