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Revert "recipes ask whether a header is there instead of inferring it… #1356

Job	Run time
lint	17s
graphics install: no side effects on unrelated members	2m 44s
select	8s
mirror-cn-reachable	25s
workspace (linux llvm 1/4)	42s
workspace (linux default 0/1)	8m 6s
workspace (linux llvm 3/4)	35s
workspace (windows default 0/1)	5m 15s
workspace (linux llvm 2/4)	57s
workspace (linux llvm 0/4)	10m 56s
workspace (macos default 0/1)	5m 51s
timings	4s
full sweep failed — open an issue	-1s
	35m 59s