Problem:    MS-Windows: clumsy way to suppress progress on CI.
Solution:   Check for "$CI" in the Makefile itself. (Ken Takata, closes #9631)

Problem:    Cannot build with dynamic Ruby 3.1.
Solution:   Add "_EXTRA" variables for CI.  Add missing functions. (Ozaki
            Kiichi, closes #9420)

Problem:    New compiler warnings from clang-12 and clang-13.
Solution:   Adjust CI and suppress some warnings. (Ozaki Kiichi, closes #9314)

Problem:    Appveyor script does not detect nmake failure.
Solution:   Explicitly check for executable. (Ken Takata, closes #8281)

Problem:    Detecting Lua version is not reliable.
Solution:   Add "vim.lua_version". (Ozaki Kiichi, closes #8080)

Problem:    Build with Ruby and clang may fail.
Solution:   Adjust congigure and sed script. (Ozaki Kiichi, closes #7566)

Problem:    Build failure with some Ruby versions.
Solution:   Adjust the code for Ruby 3.0. (Ozaki Kiichi, closes #7564)

Problem:    Github actions CI isn't used for all available platforms.
Solution:   Update the github workflows. (Ozaki Kiichi, closes #7433)

Problem:    Travis: installing snd-dummy is not always useful.
Solution:   Only install snd-dummy on amd64. (Ozaki Kiichi, closes #6738)

Problem:    MS-Windows tests on AppVeyor are slow.
Solution:   Use GitHub Actions. (Ken Takata, closes #6569)