Fix the type of `_RawOpcode` on uclibc. #3222

Job	Run time
Check (stable)	8m 23s
Check (nightly)	8m 39s
Check selected Tier 3 platforms (nightly)	4m 27s
Check nightly-only targets (nightly)	36s
Check --no-default-features (nightly)	1m 11s
Check (1.63)	21m 13s
Rustfmt	10s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 43s
Test use-libc (ubuntu)	58s
Test use-libc (i686-linux)	1m 22s
Test use-libc (aarch64-linux)	1m 28s
Test (ubuntu)	1m 4s
Test use-libc (powerpc64le-linux)	1m 23s
Test (ubuntu-20.04)	1m 5s
Test use-libc (riscv64-linux)	1m 34s
Test (i686-linux)	1m 38s
Test use-libc (arm-linux)	1m 44s
Test (aarch64-linux)	1m 45s
Test (powerpc64le-linux)	1m 35s
Test (riscv64-linux)	1m 54s
Test (s390x-linux)	1m 42s
Test (arm-linux)	1m 54s
Test (ubuntu-stable)	58s
Test (ubuntu-1.63)	3m 37s
Test (i686-linux-stable)	1m 27s
Test (aarch64-linux-stable)	1m 55s
Test (riscv64-linux-stable)	1m 46s
Test (s390x-linux-stable)	1m 45s
Test (powerpc64le-linux-stable)	1m 27s
Test (arm-linux-stable)	1m 28s
Test (ubuntu-1.63)	3m 57s
Test (i686-linux-1.63)	4m 15s
Test (aarch64-linux-1.63)	4m 38s
Test (riscv64-linux-1.63)	4m 36s
Test (s390x-linux-1.63)	4m 22s
Test (powerpc64le-linux-1.63)	5m 17s
Test (arm-linux-1.63)	4m 22s
Test (macos-latest)	1m 21s
Test (macos-11)	1m 20s
Test (windows)	1m 25s
Test (windows-2019)	1m 36s
	1h 59m 0s

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