Use Cargo's target information when possible #1927

Job	Run time
Test wasm (wasm32-unknown-unknown)	20s
Test CUDA support	22s
Clippy	8s
Test build-std (aarch64-tvos)	48s
Rustfmt	14s
MSRV (ubuntu-latest)	20s
Test build-std (aarch64-tvos-sim)	48s
Test build-std (x86_64-tvos)	49s
MSRV (windows-latest)	32s
semver-checks	8s
MSRV (macos-latest)	25s
Test (stable)	27s
Test wasm32-wasip1-thread	35s
Test (beta)	31s
Test (nightly)	32s
Test (linux32)	42s
Test (macos)	45s
Test (aarch64-macos)	41s
Test (aarch64-ios)	45s
Test (win32)	28s
Test (win64)	27s
Test (mingw32)	28s
Test (mingw64)	28s
Test (windows-2019)	28s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	27s
Test (windows-clang, windows-2019, stable, x86_64-pc-windows-msvc, clang, clang++)	28s
Test (windows-clang-cl, windows-2019, stable, x86_64-pc-windows-msvc, clang-cl, clang-cl)	29s
	13m 35s

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