Use RUSTC_WRAPPER if no other wrapper is provided #970

Job	Run time
Test CUDA support	31s
MSRV (ubuntu-latest)	19s
Test aarch64-apple-tvos	3m 9s
Clippy	19s
MSRV (windows-latest)	41s
Rustfmt	3s
Test (stable)	20s
Test (beta)	41s
Test (nightly)	25s
Test (linux32)	42s
Test (macos)	48s
Test (aarch64-ios)	56s
Test (win32)	1m 1s
Test (win64)	2m 30s
Test (mingw32)	1m 15s
Test (mingw64)	1m 37s
Test (windows-2019)	1m 42s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	2m 18s
	19m 17s

Provide feedback