stackful coroutines. #82

Job	Run time
posix (gcc-11, 2a, ubuntu-22.04)	52s
posix-cmake-install (ubuntu-22.04, OFF)	42s
posix-cmake-subdir (ubuntu-22.04, OFF)	48s
posix (gcc-12, 20,2b, ubuntu-22.04, g++-12)	1m 23s
posix-cmake-install (ubuntu-22.04, ON)	43s
posix-cmake-test (ubuntu-22.04, OFF)	1m 30s
posix-cmake-subdir (ubuntu-22.04, ON)	40s
posix (gcc-13, 20,2b, ubuntu-latest, ubuntu:23.04, g++-13)	1m 24s
posix-cmake-install (macos-13, OFF)	1m 54s
posix-cmake-test (ubuntu-22.04, ON)	1m 5s
posix-cmake-subdir (macos-13, OFF)	1m 34s
posix (clang, clang++-14, 20,2b, libc++, ubuntu-22.04, clang-14 libc++-14-dev)	1m 4s
posix-cmake-install (macos-13, ON)	1m 38s
posix-cmake-test (macos-13, OFF)	1m 48s
posix-cmake-subdir (macos-13, ON)	1m 14s
posix (clang, 20,2b, macos-13, libc++)	2m 49s
posix-cmake-test (macos-13, ON)	1m 46s
windows (msvc-14.3, 20,latest, 32,64, windows-2022)	2m 14s
windows-cmake-install (windows-2022, OFF)	3m 14s
windows (gcc, 2a, 64, windows-2019)	1m 34s
windows-cmake-subdir (windows-2022, OFF)	2m 53s
windows-cmake-install (windows-2022, ON)	3m 28s
windows-cmake-test (windows-2022, OFF)	4m 16s
windows-cmake-test (windows-2022, ON)	4m 44s
	45m 17s

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