Feature/gettext Add gettext 0.21 and add 'threads' option

[Erlkoenig90]

Specify library name and version: gettext/0.21

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

In addition to #1424, this adds a threads option to be passed to ./configure --enable-threads=X and sets it to some reasonable defaults based on the host OS. This can avoid dependencies to pthread wrappers on windows. It also updates to gettext 0.21 as at least for me, 0.20.1 doesn't cross-compile for windows.

[conan-center-bot]

Sorry, the build is only launched for Early Access Program users. You can request access writing in this issue.

[conan-center-bot]

Failure in build 2 (004b5526209a23ee9c20e7b18d04b5648ce2e74d):

• gettext/0.20.1
  • Hooks errors detected:
    • [HOOK - conan-center.py] pre_export(): ERROR: [CMAKE VERSION REQUIRED (KB-H048)] The test_packages/CMakeLists.txt requires CMake 3.1 at least. Update to 'cmake_minimum_required(VERSION 3.1)'. (https://github.com/conan-io/conan-center-index/blob/master/docs/error_knowledge_base.md#KB-H048)
    • [HOOK - conan-center.py] pre_export(): ERROR: [CONFIG.YML HAS NEW VERSION (KB-H052)] The version "0.21" exists in "conandata.yml" but not in "../config.yml", so it will not be built. Please update "../config.yml" to include newly added version "0.21". (https://github.com/conan-io/conan-center-index/blob/master/docs/error_knowledge_base.md#KB-H052)

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This pull request has been automatically closed because it has not had recent activity. Thank you for your contributions.