Set CMAKE_BUILD_PARALLEL_LEVEL to available_parallelism #1035

Job	Run time
clippy	8m 7s
Test (stable)	1m 54s
Cross build from macOS to Linux (x86_64-unknown-linux-gnu)	1m 38s
Test (arm-android)	1m 55s
Cross build from macOS to Linux (FIPS) (x86_64-unknown-linux-gnu)	5m 5s
Test (arm64-android)	1m 57s
rustfmt	25s
Test (i686-android)	1m 50s
Test features	6m 57s
Test (x86_64-android)	1m 50s
Test (aarch64-ios)	2m 22s
Test FIPS integration	2m 56s
Test (aarch64-ios-sim)	2m 16s
Test (x86_64-ios)	2m 4s
Test (i686-linux)	2m 24s
Test (arm-linux)	2m 11s
Test (aarch64-linux)	3m 18s
Test (arm64-macos)	1m 49s
Test (x86_64-macos)	2m 2s
Test (x86_64-mingw)	6m 12s
Test (i686-msvc)	5m 1s
Test (x86_64-msvc)	6m 25s
	1h 10m 38s

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