CMake

Add tests when char_t is disabled on C++20. #94

Job	Run time
build (ubuntu-latest, Debug, clang)	35s
build (ubuntu-latest, Debug, gcc)	16s
build (ubuntu-latest, Debug, tcc)	12s
build (ubuntu-latest, RelWithDebInfo, clang)	35s
build (ubuntu-latest, RelWithDebInfo, gcc)	18s
build (ubuntu-latest, RelWithDebInfo, tcc)	10s
build (ubuntu-latest, MinSizeRel, clang)	42s
build (ubuntu-latest, MinSizeRel, gcc)	18s
build (ubuntu-latest, MinSizeRel, tcc)	11s
build (ubuntu-latest, Release, clang)	41s
build (ubuntu-latest, Release, gcc)	35s
build (ubuntu-latest, Release, tcc)	29s
build (windows-latest, Debug, default)	42s
build (windows-latest, Debug, clang)	1m 8s
build (windows-latest, RelWithDebInfo, default)	42s
build (windows-latest, RelWithDebInfo, clang)	40s
build (windows-latest, MinSizeRel, default)	39s
build (windows-latest, MinSizeRel, clang)	1m 49s
build (windows-latest, Release, default)	1m 2s
build (windows-latest, Release, clang)	39s
build (macos-13, Debug, default)	22s
build (macos-13, RelWithDebInfo, default)	22s
build (macos-13, MinSizeRel, default)	21s
build (macos-13, Release, default)	32s
build (macos-latest, Debug, default)	11s
build (macos-latest, RelWithDebInfo, default)	14s
build (macos-latest, MinSizeRel, default)	8s
build (macos-latest, Release, default)	13s
	14m 46s

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