respect leading slashes in bake file path tree lookup #3108

Job	Run time
run-torture	1m 23s
build-windows-2022 (raddbg, msvc, debug)	53s
build-windows-2022 (radlink, clang, debug)	32s
build-windows-2022 (raddbg, clang, release)	2m 40s
build-windows-2022 (raddbg, clang, debug)	1m 4s
build-windows-2022 (radbin, msvc, release)	47s
build-windows-2022 (radbin, msvc, debug)	34s
build-windows-2022 (radlink, clang, release)	1m 3s
build-windows-2022 (radlink, msvc, release)	1m 2s
build-windows-2022 (radbin, clang, debug)	1m 5s
build-windows-2022 (radbin, clang, release)	2m 13s
build-windows-2022 (raddbg, msvc, release)	1m 46s
build-windows-2022 (radlink, msvc, debug)	40s
	15m 42s

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