Add CLOEXEC and NONBLOCK to pipe2

[zebreus]

Currently, our pipe2 implementation just swallows all flags, even though they work. This PR applies CLOEXEC and NONBLOCK as they are easy. CLOEXEC is tested and works.

For CLOEXEC, this is not fully POSIX-compliant because the standard requires that we set it atomically. This should not really matter for most real-world usecases.

The latest POSIX versions also include a CLOFORK flag, but we don't support it.

[Copilot]

Pull request overview

This PR updates the cloudlibc pipe2 implementation to actually apply common flags on the returned pipe file descriptors, instead of ignoring them, improving compatibility with callers (e.g., musl code paths that pass O_CLOEXEC).

Changes:

• Apply O_CLOEXEC via fcntl(..., F_SETFD, FD_CLOEXEC) on both ends of the pipe.
• Apply O_NONBLOCK via fcntl(..., F_SETFL, O_NONBLOCK) on both ends of the pipe.
• Add <fcntl.h> include to support the new flag handling.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

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