Fall back to `TCGETS` if `TCGETS2` fails #4208

Job	Run time
Check selected Tier 3 platforms (nightly)	4m 42s
Check --no-default-features (nightly)	53s
Check (stable)	6m 15s
Check nightly-only targets (nightly)	25s
Check (nightly)	6m 15s
Rustfmt	5s
Check (1.63)	11m 6s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 12s
Test (ubuntu)	42s
Test (ubuntu-20.04)	41s
Test use-libc (ubuntu)	38s
Test (i686-linux)	1m 6s
Test use-libc (i686-linux)	53s
Test (aarch64-linux)	1m 12s
Test use-libc (aarch64-linux)	59s
Test use-libc (powerpc64le-linux)	58s
Test (powerpc64le-linux)	1m 2s
Test (riscv64-linux)	1m 1s
Test use-libc (riscv64-linux)	1m 10s
Test (s390x-linux)	1m 8s
Test use-libc (arm-linux)	57s
Test (arm-linux)	1m 9s
Test (ubuntu-stable)	38s
Test (i686-linux-stable)	1m 1s
Test (aarch64-linux-stable)	1m 2s
Test (riscv64-linux-stable)	58s
Test (s390x-linux-stable)	1m 22s
Test (powerpc64le-linux-stable)	1m 6s
Test (arm-linux-stable)	1m 6s
Test (ubuntu-1.63)	3m 33s
Test (i686-linux-1.63)	3m 48s
Test (aarch64-linux-1.63)	4m 2s
Test (riscv64-linux-1.63)	3m 55s
Test (s390x-linux-1.63)	3m 57s
Test (powerpc64le-linux-1.63)	4m 5s
Test (arm-linux-1.63)	4m 4s
Test (macos-latest)	17m 45s
Test (macos-12)	18m 43s
Test (windows)	43s
Test (windows-2019)	58s
Test (musl)	40s
	1h 57m 55s

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