Travis osx, OpenMP using llvm clang 12.0.1 gives linking errors

[robbietuk]

In two different PR's #901 and #902, the osx, OpenMP, using llvm clang builds are failing, see https://app.travis-ci.com/github/UCL/STIR/jobs/525748509. But it is only this build configuration, all others pass.

[robbietuk]

This is a seperate travis macOS issue to that discussed in #897

[KrisThielemans]

error is https://app.travis-ci.com/github/UCL/STIR/jobs/532976171#L8622

Undefined symbols for architecture x86_64:
  "stir::BinNormalisation::set_up(std::__1::shared_ptr<stir::ExamInfo const> const&, std::__1::shared_ptr<stir::ProjDataInfo const> const&)", referenced from:
      vtable for stir::TrivialBinNormalisation in liblistmode_buildblock.a(LmToProjData.cxx.o)
  "stir::BinNormalisation::BinNormalisation()", referenced from:
      stir::LmToProjData::set_defaults() in liblistmode_buildblock.a(LmToProjData.cxx.o)
  "stir::BinNormalisation::~BinNormalisation()", referenced from:
      stir::LmToProjData::set_defaults() in liblistmode_buildblock.a(LmToProjData.cxx.o)
      stir::TrivialBinNormalisation::~TrivialBinNormalisation() in liblistmode_buildblock.a(LmToProjData.cxx.o)
      stir::TrivialBinNormalisation::~TrivialBinNormalisation() in liblistmode_buildblock.a(LmToProjData.cxx.o)
  "stir::TrivialBinNormalisation::registered_name", referenced from:
      stir::RegisteredParsingObject<stir::TrivialBinNormalisation, stir::BinNormalisation, stir::BinNormalisation>::get_registered_name() const in liblistmode_buildblock.a(LmToProjData.cxx.o)
  "stir::BinNormalisation::check(stir::ProjDataInfo const&) const", referenced from:
      vtable for stir::TrivialBinNormalisation in liblistmode_buildblock.a(LmToProjData.cxx.o)
  "stir::BinNormalisation::check(stir::ExamInfo const&) const", referenced from:
      vtable for stir::TrivialBinNormalisation in liblistmode_buildblock.a(LmToProjData.cxx.o)
  "typeinfo for stir::BinNormalisation", referenced from:
      typeinfo for stir::RegisteredParsingObject<stir::TrivialBinNormalisation, stir::BinNormalisation, stir::BinNormalisation> 

[KrisThielemans]

Last succesful build was in #902 and used LLVM Clang 12.0.0. All subsequent builds failed for this job, and used LLVM Clang 12.0.1

[KrisThielemans]

disabled this job in 8a2e4ea50be0b690957bf831ba53f196f8c40534 as it makes all PR CI fail

[KrisThielemans]

presumably outdated

[KrisThielemans]

indeed outdated with clang 16, tested in https://github.com/UCL/STIR/pull/1198 (the relevant job failed because of a run-time problem #1200, no linking error)