Add more signal constants for NuttX

[no1wudi]

Description

Add more signal constants for NuttX

Sources

https://github.com/apache/nuttx/blob/master/include/signal.h

https://github.com/apache/nuttx/blob/e0b221016f726b9e187b28baa04d601b0e8829e5/include/signal.h#L141-L175

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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[no1wudi]

@rustbot label +stable-nominated