[AdamMagued]

Description

When Node.js initializes stdio streams (such as evaluating process.stdout or process.stderr), libuv sets O_NONBLOCK on the underlying open file descriptions for standard descriptors 0, 1, and 2.

In src/node_process_methods.cc, Execve() clears FD_CLOEXEC on file descriptors 0-2 so they persist across execve(2). However, Execve() bypasses the normal process exit sequence that invokes ResetStdio(). Consequently, the replacement binary executed via process.execve() inherits file descriptors 0-2 in non-blocking mode. Programs assuming blocking stdio (such as python3, cat, or yes) fail with EAGAIN (Resource temporarily unavailable) once a pipe buffer fills up.

This change:

1. Clears O_NONBLOCK on standard streams (descriptors 0, 1, and 2) before calling execve(2), matching the blocking stdio behavior provided to child processes in child_process.spawn().
2. Restores the original F_GETFL file status flags alongside FD_CLOEXEC if execve(2) fails, preserving the invariant that a failed process.execve() leaves no observable side effects before throwing to JavaScript.
3. Adds automated regression tests in test/parallel/test-process-execve-stdio-blocking.js verifying that a program executed via process.execve() receives blocking stdio across fds 0-2 and completes writes that exceed pipe buffer capacity without EAGAIN.

Fixes: #66824

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