Restore target build dir behavior for Xcode. Closes #8321 #1452

Job	Run time
build-emscripten (emscripten)	3m 21s
build-msys2 (mingw64)	4m 24s
rpi-build (aarch64, arm64, aarch64-linux-gnu, 1)	1m 55s
build-msys2 (clang64)	4m 10s
build-vs2019 (x64)	1m 24s
build-macos (osx, makefiles)	1m 36s
build-ios-tvos (ios, macos)	2m 4s
build-msys2 (ucrt64)	4m 24s
build-vs2022 (ARM64EC)	13m 33s
build-vs2022 (x64)	12m 8s
build-macos (osx, xcode)	1m 4s
build-ios-tvos (tvos, macos)	3m 2s
build-linux64 (linux64, 64gcc6)	3m 13s
build-vs2022 (ARM64)	12m 20s
rpi-build (armv6l, armhf, arm-linux-gnueabihf, 1)	1m 58s
	1h 10m 36s

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