[MacPorts] #69578: abseil @ 20240116.1: Update cxx_standard to 2017

[MacPorts]

#69578: abseil @ 20240116.1: Update cxx_standard to 2017
---------------------------+----------------------
  Reporter:  FlyingSamson  |      Owner:  judaew
      Type:  enhancement   |     Status:  assigned
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:  2.9.1
Resolution:                |   Keywords:
      Port:  abseil        |
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Comment (by FlyingSamson):

 Yes, I fear abseil itself is required to be compiled with c++17 standard.
 Because if it is compiled with c++14 standard, it declares its own
 implementation of `absl::string_view` which cannot provide an implicit
 conversion to `std::string_view` as this type only exists since c++17.
 Then compiling or-tool will fail as an assignment of abseil's own
 `absl::string_view` to an `std::string` is not possible.

 If you would rather not update abseil to c++17 yet, I could also try
 patching or-tools to assign the contents of the `absl::string_views` to
 the `std::string` variable (replicating the standard's implementation of
 `std::string::operator=(std::string_view)`, but I fear that would result
 in a quite large patch set. Therefor, I thought I ask first if it would be
 acceptable to update the c++ standard used to compile abseil, instead.

-- 
Ticket URL: <https://trac.macports.org/ticket/69578#comment:3>
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