fix: add uclibc MIPS signal flags compatibility #2111

Job	Run time
aarch64_linux_native_builds (aarch64-unknown-linux-gnu)	20s
macos-aarch64	24s
macos	23s
x86_64_linux_native_builds (x86_64-unknown-linux-gnu)	13s
aarch64_linux_native_builds (aarch64-unknown-linux-musl)	26s
minver	15s
solaris (x86_64-pc-solaris)	5m 43s
rust_stable	1m 36s
tier3 (x86_64-unknown-openbsd)	45s
x86_64_linux_native_builds (x86_64-unknown-linux-musl)	16s
rustfmt	9s
tier3 (x86_64-unknown-haiku)	45s
tier3 (armv7-unknown-linux-uclibceabihf)	46s
tier3 (x86_64-unknown-dragonfly)	42s
redox	-1s
cross_compiling	-1s
cross	-1s
	12m 40s

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