linux

Add hardening flags to linux targets #4328

Job	Run time
Generate build matrix	10s
crate / x86_64	1m 50s
image / x86_64 / build	1m 3s
crate / aarch64	1m 4s
image / x86_64 / build.cross-riscv64	1m 6s
image / x86_64 / build.cross	55s
image / x86_64 / gcc	1m 37s
x86_64-unknown-linux-musl / 3.14 / lto+static	15m 27s
x86_64-unknown-linux-gnu / 3.14 / freethreaded+pgo+lto	19m 23s
x86_64-unknown-linux-gnu / 3.14 / pgo+lto	18m 29s
x86_64-unknown-linux-musl / 3.14 / freethreaded+lto	16m 26s
x86_64-unknown-linux-musl / 3.14 / lto	15m 39s
armv7-unknown-linux-gnueabihf / 3.14 / lto	12m 10s
	1h 45m 19s

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