Fix missing SO_* values

[snogge]

Some identifiers for #4148 was missing, and this was not detected because verify-build does not rebuild when
RUST_LIBC_UNSTABLE_LINUX_TIME_BITS64=1 is set.

Fix the verify-build task by using a separate target-dir and add the missing identifiers

This is probably not the best way of structuring the CI steps, it could also be set up using a matrix in the verify-build task of ci.yml.

Sources

https://github.com/torvalds/linux/blob/master/arch/mips/include/uapi/asm/socket.h#L125
https://github.com/torvalds/linux/blob/master/arch/powerpc/include/uapi/asm/socket.h
https://github.com/torvalds/linux/blob/master/tools/include/uapi/asm-generic/socket.h

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]

r? @tgross35

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