[libltdl] New port

[dg0yt]

• What does your PR fix?

  Adds an explicit libltdl port. This mirrors the packaging in other repositories:
  https://repology.org/project/libltdl/information
  Some ports already use individual copies.
  [libtool,libltdl] New port #21731 (comment), CC @vividos

  Known issues:
  When using libltdl with static linkage for linux, libdl (-ldl) is a usage requirement. Some downstream ports don't handle this sufficiently. (Static linkage is less common in linux.) CMAKE_DL_LIBS seems to be a good source of polyfill for CMake projects.

• Which triplets are supported/not supported? Have you updated the CI baseline?

  !uwp, no

• Does your PR follow the maintainer guide?

  yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

  yes

[dg0yt]

To be continued after #27314.

[github-actions]

You have modified or added at least one portfile where deprecated functions are used.

If you feel able to do so, please consider migrating them to the new functions:
vcpkg_install_cmake -> vcpkg_cmake_install (from port vcpkg-cmake)
vcpkg_build_cmake -> vcpkg_cmake_build (from port vcpkg-cmake)
vcpkg_configure_cmake -> vcpkg_cmake_configure (Please remove the option PREFER_NINJA) (from port vcpkg-cmake)
vcpkg_fixup_cmake_targets -> vcpkg_cmake_config_fixup (from port vcpkg-cmake-config)
vcpkg_extract_source_archive_ex -> vcpkg_extract_source_archive
vcpkg_build_msbuild -> vcpkg_install_msbuild
vcpkg_copy_tool_dependencies -> vcpkg_copy_tools
vcpkg_apply_patches should be replaced by the PATCHES arguments to the "extract" helpers (e.g. vcpkg_from_github())

In the ports that use the new function, you have to add the corresponding dependencies:

{
  "name": "vcpkg-cmake",
  "host": true
},
{
  "name": "vcpkg-cmake-config",
  "host": true
}

The following files are affected:

• ports/libltdl/portfile.cmake

[dg0yt]

You have modified or added at least one portfile where deprecated functions are used.
...
In the ports that use the new function, you have to add the corresponding dependencies:

@autoantwort Now it catches vcpkg_extract_source_archive_ex but the suggested dependencies do no match. Maybe we should just point to a doc page with detailed instructions?

[dg0yt]

#27314 was merged. PR updated.

[autoantwort]

Now it catches vcpkg_extract_source_archive_ex but the suggested dependencies do no match.

What do you mean?

[dg0yt]

Modernizing vcpkg_extract_source_archive_ex doesn't need the proposed vcpkg-cmake, vcpkg-cmake-config.

[autoantwort]

Yeah it does not check which function is used, it checks if any function is used. In general the goal should be #26981

[github-actions]

You have modified or added at least one portfile where deprecated functions are used.

If you feel able to do so, please consider migrating them to the new functions:
vcpkg_install_cmake -> vcpkg_cmake_install (from port vcpkg-cmake)
vcpkg_build_cmake -> vcpkg_cmake_build (from port vcpkg-cmake)
vcpkg_configure_cmake -> vcpkg_cmake_configure (Please remove the option PREFER_NINJA) (from port vcpkg-cmake)
vcpkg_fixup_cmake_targets -> vcpkg_cmake_config_fixup (from port vcpkg-cmake-config)
vcpkg_extract_source_archive_ex -> vcpkg_extract_source_archive
vcpkg_build_msbuild -> vcpkg_install_msbuild
vcpkg_copy_tool_dependencies -> vcpkg_copy_tools
vcpkg_apply_patches should be replaced by the PATCHES arguments to the "extract" helpers (e.g. vcpkg_from_github())

In the ports that use the new function, you have to add the corresponding dependencies:

{
  "name": "vcpkg-cmake",
  "host": true
},
{
  "name": "vcpkg-cmake-config",
  "host": true
}

The following files are affected:

• ports/libltdl/portfile.cmake

[dg0yt]

To be continued after #27471.

[BillyONeal]

Closing this as it's been in draft without changes for more than a year, please feel to recreate or reopen!