Merge hebasto/bitcoin#302: cmake: Ignore build subdirectories within … #2804

Job	Run time
Win64 native, VS 2022	1h 27m 44s
macOS 13 native, x86_64, no depends, sqlite only, gui	51m 59s
test each commit	0s
ASan + LSan + UBSan + integer, no depends, USDT	39m 59s
	2h 59m 42s

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