Use relative directory for obj files hash #2007

Job	Run time
Clippy	16s
Test CUDA support	24s
Test build-std (aarch64-tvos)	2m 36s
Test wasm (wasm32-unknown-unknown)	12s
Test build-std (aarch64-tvos-sim)	1m 49s
Test build-std (x86_64-tvos)	1m 43s
Rustfmt	5s
semver-checks	15s
MSRV (ubuntu-latest)	25s
MSRV (windows-latest)	50s
Test wasm32-wasip1-thread	27s
MSRV (macos-latest)	29s
Test (stable)	1m 30s
Test (beta)	1m 20s
Test (nightly)	1m 21s
Test (linux32)	2m 10s
Test (macos)	3m 21s
Test (aarch64-macos)	2m 45s
Test (aarch64-ios)	1m 22s
Test (win32)	3m 13s
Test (win64)	3m 51s
Test (mingw32)	4m 11s
Test (mingw64)	3m 28s
Test (windows-2019)	2m 47s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	3m 59s
Test (windows-clang, windows-2019, stable, x86_64-pc-windows-msvc, clang, clang++)	7m 9s
Test (windows-clang-cl, windows-2019, stable, x86_64-pc-windows-msvc, clang-cl, clang-cl)	7m 13s
	59m 11s

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