CMake

Add support for C++20 without char8_t #90

Job	Run time
build (ubuntu-latest, Debug, clang)	11s
build (ubuntu-latest, Debug, gcc)	14s
build (ubuntu-latest, Debug, tcc)	11s
build (ubuntu-latest, RelWithDebInfo, clang)	19s
build (ubuntu-latest, RelWithDebInfo, gcc)	25s
build (ubuntu-latest, RelWithDebInfo, tcc)	18s
build (ubuntu-latest, MinSizeRel, clang)	17s
build (ubuntu-latest, MinSizeRel, gcc)	19s
build (ubuntu-latest, MinSizeRel, tcc)	10s
build (ubuntu-latest, Release, clang)	17s
build (ubuntu-latest, Release, gcc)	13s
build (ubuntu-latest, Release, tcc)	13s
build (windows-latest, Debug, default)	57s
build (windows-latest, Debug, clang)	1m 28s
build (windows-latest, RelWithDebInfo, default)	1m 16s
build (windows-latest, RelWithDebInfo, clang)	1m 47s
build (windows-latest, MinSizeRel, default)	35s
build (windows-latest, MinSizeRel, clang)	1m 51s
build (windows-latest, Release, default)	51s
build (windows-latest, Release, clang)	2m 0s
build (macos-13, Debug, default)	21s
build (macos-13, RelWithDebInfo, default)	19s
build (macos-13, MinSizeRel, default)	20s
build (macos-13, Release, default)	23s
build (macos-latest, Debug, default)	9s
build (macos-latest, RelWithDebInfo, default)	12s
build (macos-latest, MinSizeRel, default)	13s
build (macos-latest, Release, default)	9s
	15m 58s

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