PR Summary: Fix Duplicate Output from fork()

[yashaswi2000]

This PR addresses an issue where the output from a program using the fork() system call was duplicated, resulting in unintended output. The problem was due to both the parent and child processes having the same iO buffers causing both to print to the standard output.

To resolve this, the following changes were made:

• Added fflush(stdout); before the fork() call to ensure that the buffer is flushed, preventing any buffered output from being duplicated in the child process.

• With these changes, the program now produces the correct and intended output, ensuring only the parent process prints "2!" while the child process exits immediately.

Issue link: Lind-Project/native_client#12

[JustinCappos]

Does this problem only exist for stdout / stderr? What if they are duped to new fds? Do those need to be flushed as well / intead? What if stdout and stderr are redirected to new types of output (not the terminal)?

Can we add some tests for these cases?