Darwin: Implement sysroot flag #140

Job	Run time
Test / Linux (nightly-main - jammy - x86_64)	6m 9s
Test / Linux (nightly-6.3 - jammy - x86_64)	6m 0s
Test / macOS (Xcode 26.0 - tahoe - ARM64)	2m 51s
Test / Windows (nightly-main - windows-2022)	21m 4s
Soundness / Documentation check	35s
Soundness / Broken symlinks check	5s
Soundness / Shell check	24s
Soundness / YAML lint check	0s
Soundness / Format check	0s
Soundness / License headers check	0s
Soundness / API breakage check	0s
Soundness / Unacceptable language check	0s
Soundness / Python lint check	0s
Soundness / Documentation check (macOS)	0s
	37m 8s

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