Mark ctr and xer as clobbered in powerpc/powerpc64 syscalls #5413

Job	Run time
Check --no-default-features (nightly-2025-06-23)	1m 0s
Rustfmt	15s
Check nightly-only targets (nightly-2025-06-23)	42s
Check (nightly-2025-06-23)	1m 45s
Check selected Tier 3 platforms (nightly-2025-06-23)	6m 11s
Check (1.63)	1m 57s
Test rustix_use_experimental_asm (powerpc64le-linux)	2m 49s
Check (stable)	1m 43s
Test rustix_use_experimental_asm (powerpc-linux)	2m 38s
Test use-libc (powerpc-linux)	47s
Test use-libc (s390x-linux)	46s
Test use-libc (arm-linux)	47s
Test use-libc (aarch64-linux)	46s
Test use-libc (riscv64-linux)	45s
Test use-libc (powerpc64le-linux)	34s
Test rustix_use_experimental_asm (s390x-linux)	1m 32s
Test use-libc (ubuntu)	32s
Test use-libc (i686-linux)	47s
Test (arm-linux)	46s
Test (s390x-linux-stable)	48s
Test (powerpc-linux)	46s
Test (ubuntu-22.04)	46s
Test (ubuntu-stable)	33s
Test (i686-linux)	46s
Test (aarch64-linux-stable)	46s
Test (powerpc64le-linux)	46s
Test (i686-linux-stable)	47s
Test (s390x-linux)	46s
Test (powerpc64le-linux-stable)	47s
Test (aarch64-linux)	47s
Test (powerpc-linux-stable)	47s
Test (macos-13)	48s
Test (arm-linux-stable)	46s
Test (ubuntu)	46s
Test (arm-linux-1.63)	47s
Test (riscv64-linux-1.63)	46s
Test (riscv64-linux)	47s
Test (windows)	39s
Test (macos-latest)	40s
Test (riscv64-linux-stable)	47s
Test (ubuntu-1.63)	46s
Test (powerpc64le-linux-1.63)	46s
Test (powerpc64le-linux)	46s
Test (powerpc-linux-1.63, ubuntu-latest, 1.63, powerpc-unknown-linux-gnu, gcc-powerpc-linux-gnu, ...	35s
Test (aarch64-linux-1.63)	47s
Test (i686-linux-1.63)	47s
Test (s390x-linux-1.63)	47s
Test (musl)	38s
	48m 45s

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