Fix the name of `c_ispeed`/`c_ospeed` on powerpc musl targets. (#1158) #4230

Job	Run time
Check selected Tier 3 platforms (nightly)	35s
Check (stable)	1m 22s
Check --no-default-features (nightly)	55s
Check nightly-only targets (nightly)	23s
Check (nightly)	1m 17s
Rustfmt	12s
Check (1.63)	1m 35s
Test (ubuntu)	25s
Test use-libc (ubuntu)	47s
Test rustix_use_experimental_asm (powerpc64le-linux)	51s
Test (ubuntu-20.04)	25s
Test use-libc (i686-linux)	1m 4s
Test use-libc (aarch64-linux)	2m 2s
Test (i686-linux)	34s
Test use-libc (powerpc64le-linux)	1m 15s
Test (aarch64-linux)	32s
Test use-libc (riscv64-linux)	1m 11s
Test (powerpc64le-linux)	40s
Test use-libc (arm-linux)	1m 10s
Test (riscv64-linux)	41s
Test (s390x-linux)	40s
Test (arm-linux)	40s
Test (ubuntu-stable)	40s
Test (i686-linux-stable)	44s
Test (aarch64-linux-stable)	45s
Test (riscv64-linux-stable)	44s
Test (s390x-linux-stable)	43s
Test (powerpc64le-linux-stable)	33s
Test (arm-linux-stable)	44s
Test (ubuntu-1.63)	40s
Test (i686-linux-1.63)	42s
Test (aarch64-linux-1.63)	43s
Test (riscv64-linux-1.63)	41s
Test (s390x-linux-1.63)	33s
Test (powerpc64le-linux-1.63)	35s
Test (arm-linux-1.63)	45s
Test (macos-latest)	5m 29s
Test (macos-12)	28s
Test (windows)	26s
Test (windows-2019)	27s
Test (musl)	41s
	36m 19s

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