Make `ENDL` optional like `ENDSECTION` #3930

Job	Run time
windows-mingw-build (32)	1m 11s
windows (32, windows-2019)	6m 16s
windows-mingw-build (64)	1m 0s
unix (ubuntu-20.04, g++, make)	5m 16s
windows (32, windows-2022)	5m 11s
unix (ubuntu-20.04, g++, cmake)	5m 26s
windows (64, windows-2019)	6m 14s
unix (ubuntu-20.04, clang++, make)	6m 2s
windows (64, windows-2022)	5m 11s
macos-static	2m 2s
unix (ubuntu-20.04, clang++, cmake)	6m 4s
unix (ubuntu-22.04, g++, make)	5m 33s
unix (ubuntu-22.04, g++, cmake)	5m 42s
unix (ubuntu-22.04, clang++, make)	3m 50s
unix (ubuntu-22.04, clang++, cmake)	4m 6s
unix (macos-14, clang++, make)	6m 10s
unix (macos-14, clang++, cmake)	6m 6s
windows-mingw-testing (windows-2019, 32)	4m 50s
windows-mingw-testing (windows-2019, 64)	5m 0s
windows-mingw-testing (windows-2022, 32)	4m 24s
windows-mingw-testing (windows-2022, 64)	3m 55s
	1h 39m 29s

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