initial support fallback #3614

Job	Run time
Ubuntu / Release / gcc	22m 34s
macOS / Release / homebrew-clang	6m 46s
Ubuntu / Debug / gcc	18m 58s
Windows / Release / cl	29m 18s
macOS / Debug / homebrew-clang	7m 3s
Ubuntu / Release / clang	19m 25s
Windows / Release / clang	20m 21s
macOS / Release / system-clang	5m 39s
macOS / Debug / system-clang	6m 33s
Ubuntu / Debug / clang	17m 58s
Windows / Release / clang-cl	19m 40s
Windows / Debug / cl	19m 38s
Windows / Debug / clang	28m 9s
Windows / Debug / clang-cl	24m 20s
	4h 6m 22s

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