Qt6: improve cross-compilation support, misc minor fixes

[valgur]

Summary

Changes to recipe: qt/6.x.x

Motivation

#26529 added the core logic that's necessary to cross-compiler the Qt6 recipe at all, but it still has some major limitations:

• Optional modules that build and rely on their own tools require these to be provided by the host-context Qt instead for the build to work. This PR propagates the necessary options to the Qt tool_requires.
• The Qt CMake modules in the host context try to use the host-context executables when defining targets like Qt6::moc, this can either fail if these have not been built and are useless for consuming projects trying to use these tools.
• Consuming projects currently need to set CMAKE_AUTOMOC_EXECUTABLE etc. variables for CMake to find the correct build-context tools.

Details

In addition to fixing the above issues, this PR also incorporates a few other fixes that I've accumulated in the process of improving cross-compilation support for all optional modules in Qt. These include:

• made force_build_tools optional and False by default for cross-compilation, since they are generally not useful in that context and can have build issues:

  Linking against shared libraries appears to have issues, potentially due to mixed native and cross-compiled libs.

  [1409/1453] Linking CXX executable qtbase/libexec/rcc
  FAILED: qtbase/libexec/rcc
  : && /usr/bin/aarch64-linux-gnu-g++-13 -DNDEBUG -O2 -Wl,-z,relro,-z,now -Wl,--enable-new-dtags -fPIE -pie qtbase/src/tools/rcc/CMakeFiles/rcc_native.dir/rcc_native_autogen/mocs_compilation.cpp.o qtbase/src/tools/rcc/CMakeFiles/rcc_native.dir/main.cpp.o qtbase/src/tools/rcc/CMakeFiles/rcc_native.dir/rcc.cpp.o -o qtbase/libexec/rcc  -Wl,-rpath,/home/user/.conan2/p/b/qtc8d3483cfcb1b/b/build/Release/qtbase/lib:  qtbase/lib/libQt6Core.so.6.8.2 && :
  /usr/lib/gcc-cross/aarch64-linux-gnu/13/../../../../aarch64-linux-gnu/bin/ld: warning: libicudata.so.75, needed by /home/user/.conan2/p/b/icu9b438096da10d/p/lib/libicuuc.so.75, not found (try using -rpath or -rpath-link)
  /usr/lib/gcc-cross/aarch64-linux-gnu/13/../../../../aarch64-linux-gnu/bin/ld: /home/user/.conan2/p/b/icu9b438096da10d/p/lib/libicuuc.so.75: undefined reference to `icudt75_dat'
  collect2: error: ld returned 1 exit status

• Dropped cross_compile and sysroot options since these seem to be solely there as carry-overs from the Qt5 recipe this one was based on. These were effectively useless before the cross-compilation support and are unlikely to have ever been used. The cross_compile option has little value now that the recipe has cross-compilation support and sysroot should use the value from tools.build:sysroot instead. These could be added back if someone sees a need for them.

• add missing package_type and a missing fPIC option.

• Added an option for unity build, which can help with build times quite a bit. I did not remove it from package_id, though, since it can cause subtle differences in the built binaries.

• Dropped some validation checks and workarounds which appear likely to be outdated or possibly only relevant for Conan v1.

• Added a transitive_libs=True for opengl/system.

• gssapi/krb5 is now supported on CCI (although the exported .pc files are not correct: krb5: set pkg_config_name #25434).

• Added all executables built and installed by Qt to package() and refactored it a bit.

• Improved the filtering for kept .cmake module files in package().

• No need to remove *.la files for a CMake project.

• Export QT_HOST_PATH and QT_HOST_PATH_CMAKE_DIR env vars for host-context Qt. These are used to find the correct executables.

---

• Read the contributing guidelines
• Checked that this PR is not a duplicate: list of PRs by recipe
• Tested locally with at least one configuration using a recent version of Conan

[valgur]

Logs for Qt and ConanCenter recipes that consume Qt by default.

Cross-compiled using gcc-13-aarch64-linux-gnu: https://gist.github.com/valgur/5a550530a55b0df98016b89dbb25d861

The consuming recipes have any necessary fixes applied, such as using CMake >= 3.27 for the Qt CMake vars to work correctly. The Qt recipe has some additional fixes applied as well, such as support for relocated non-system X11.

daggy-shared.log
daggy-static.log
limereport-shared.log - Failed to find the host tool "Qt6::qhelpgenerator"
limereport-static.log - Failed to find the host tool "Qt6::qhelpgenerator"
mocknetworkaccessmanager-shared.log
mocknetworkaccessmanager-static.log
qarchive-shared.log
qarchive-static.log
qcoro-shared.log *
qcoro-static.log *
qcustomplot-shared.log *
qcustomplot-static.log
qscintilla-shared.log
qscintilla-static.log
qt-advanced-docking-system-shared.log - test_package Qt linker error
qt-advanced-docking-system-static.log
qtawesome-shared.log *
qtawesome-static.log
qt-shared.log *
qt-static.log
qwt-shared.log *
qwt-static.log
qxlsx-shared.log*
qxlsx-static.log
qxmpp-shared.log
qxmpp-static.log
runtimeqml-shared.log - linking of qml executable fails, probably due to [replace_requires] of X11
runtimeqml-static.log
spix-shared.log - linking of qml executable fails, probably due to [replace_requires] of X11
spix-static.log

* - test_package fails due to what seems to be a bug in [replace_requires] not propagating transitive headers/libraries correctly in some cases