Add the TCP_FUNCTION_BLK and TCP_FUNCTION_ALIAS socket options

[asomers]

For FreeBSD only

Description

These two socket options are used to get and set a socket's TCP stack, on FreeBSD only.

Sources

https://man.freebsd.org/cgi/man.cgi?query=tcp
https://github.com/freebsd/freebsd-src/blob/976e1d36be688166e140cbaded01d433c61e6d47/sys/netinet/tcp.h#L229

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[rustbot]

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[asomers]

The error looks unrelated to my change. For one thing, it was a Linux build that failed. For another, this is the error:

rustc-LLVM ERROR: Cannot select: 0x7fe87eb15000: f32,ch = load<(load (s16) from %ir.0), anyext from f16> 0x7fe87eb15a10, 0x7fe87eaf6540, undef:i64, src/fmt/float.rs:238:30
  0x7fe87eaf6540: i64,ch = CopyFromReg 0x7fe87eabb468, Register:i64 %0
    0x7fe87eb15af0: i64 = Register %0
  0x7fe87eb155b0: i64 = undef
In function: _ZN4core3fmt5float50_$LT$impl$u20$core..fmt..Debug$u20$for$u20$f16$GT$3fmt17h9203c7e9bc0be64fE
error: could not compile `core` (lib)

[tgross35]

The error looks unrelated to my change. For one thing, it was a Linux build that failed. For another, this is the error:

rustc-LLVM ERROR: Cannot select: 0x7fe87eb15000: f32,ch = load<(load (s16) from %ir.0), anyext from f16> 0x7fe87eb15a10, 0x7fe87eaf6540, undef:i64, src/fmt/float.rs:238:30
  0x7fe87eaf6540: i64,ch = CopyFromReg 0x7fe87eabb468, Register:i64 %0
    0x7fe87eb15af0: i64 = Register %0
  0x7fe87eb155b0: i64 = undef
In function: _ZN4core3fmt5float50_$LT$impl$u20$core..fmt..Debug$u20$for$u20$f16$GT$3fmt17h9203c7e9bc0be64fE
error: could not compile `core` (lib)

That was just a bug on the most recent nightly, I think it should be fixed with the one that just released.

@rustbot label +stable-nominated