Add target selector #5946

Job	Run time
build test linux x86-64	3m 9s
check-rust	4m 6s
build test windows x86-64	5m 18s
check-website	9s
scarb-metadata compatibility check	37s
doc tests	3m 3s
test linux x86-64 1/8	6m 21s
test linux x86-64 2/8	8m 4s
test linux x86-64 3/8	8m 31s
test linux x86-64 4/8	5m 41s
test linux x86-64 5/8	5m 28s
test linux x86-64 6/8	4m 12s
test linux x86-64 7/8	4m 39s
test linux x86-64 8/8	3m 16s
test windows x86-64 1/8	6m 58s
test windows x86-64 2/8	7m 38s
test windows x86-64 3/8	7m 34s
test windows x86-64 4/8	6m 11s
test windows x86-64 5/8	6m 28s
test windows x86-64 6/8	4m 36s
test windows x86-64 7/8	6m 28s
test windows x86-64 8/8	3m 59s
	1h 52m 26s

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