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recipes ask whether a header is there instead of inferring it from th… #1355

Job	Run time
lint	13s
graphics install: no side effects on unrelated members	2m 55s
select	31s
mirror-cn-reachable	21s
workspace (linux llvm 2/4)	38s
workspace (linux default 0/1)	8m 18s
workspace (windows default 0/1)	5m 9s
workspace (linux llvm 1/4)	38s
workspace (linux llvm 3/4)	51s
workspace (linux llvm 0/4)	8m 41s
workspace (macos default 0/1)	5m 3s
timings	4s
full sweep failed — open an issue	0s
	33m 22s