poppler-qt5: CMake-related build failure on 10.8

[mojca (Mojca Miklavec)]

Build of poppler on 10.8 fails in a pretty absurd way:

-- Configuring done
CMake Error in qt5/src/CMakeLists.txt:
  No known features for CXX compiler

  "Clang"

  version 5.0.2.

​https://build.macports.org/builders/ports-10.8_x86_64_legacy-builder/builds/71069

Weird enough it works on 10.7.

[ryandesign (Ryan Carsten Schmidt)]

It's easy enough to reproduce this on a newer system such as High Sierra with:

sudo port configure poppler-qt5 configure.compiler=macports-clang-6.0

[kencu (Ken)]

Looks like a known issue. See:

<​https://stackoverflow.com/questions/38027292/configure-a-qt5-5-7-application-for-android-with-cmake/40256862#40256862>

and

<​https://bugreports.qt.io/browse/QTBUG-54666>

and in particular

<​https://bugreports.qt.io/browse/QTBUG-57886>

I tried the suggested workaround, it it got past the initial issue, but then it died later with unrecognized compiler characteristics.

This issue seems to be happening in a number of different tickets, and we should probably condense it into one to follow it along.

[yan12125 (Chih-Hsuan Yen)]

This should be fixed with a simple patch for poppler:

​https://github.com/macports/macports-ports/pull/3098#issuecomment-443080512

[kencu (Ken)]

Ah, just came down to improperly-written CMakeLists.txt files in the end. Seems a common enough problem out there that I'm surprised to see it still on the qt bug tracker. The cmake docs are clear enough that the requirements have to come first...good job nailing it.

[dbevans (David B. Evans)]

In 652319c36aed7b50ae11beef623b0f1cb66a914c/macports-ports (master):

poppler-qt5: fix cmake/qt5 configuration failures with non-Apple clang

Closes #57167