[MacPorts] #69975: re2 @2024-04-01_2: fails to build on macOS 10.12/Xcode 9.2 due to <optional> not found in abseil headers

[MacPorts]

#69975: re2 @2024-04-01_2: fails to build on macOS 10.12/Xcode 9.2 due to
<optional> not found in abseil headers
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  Reporter:  andlabs  |      Owner:  herbygillot
      Type:  defect   |     Status:  assigned
  Priority:  Normal   |  Milestone:
 Component:  ports    |    Version:  2.9.3
Resolution:           |   Keywords:
      Port:  re2      |
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Comment (by FlyingSamson):

 In theory yes. But in the end the availability of a features also depends
 on whether it was implemented in the specific compiler. The
 [https://en.cppreference.com/w/cpp/compiler_support/17 compiler support
 list] lists `std::optional` as available since apple clang 10.0.0. Does
 the `/usr/bin/clang++` shown in your log meet this version requirement?

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Ticket URL: <https://trac.macports.org/ticket/69975#comment:3>
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