Retry interrupted std stream read/write calls.

[LostBranch5502]

The Hashlink profiler causes some Linux system calls to be interrupted. Previously, error handling was added for std/file.c read/write operations. However, the read/write calls made by sys.io.Process use instead the unistd read/write functions which are also affected by the interrupts.

This pull request extends the previously introduced error handling also to the unistd read/write calls in std/process.c.

The behaviour can be tested with the following program, which uses the stdout, stderr and stdin streams via sys.io.Process:

import sys.io.Process;

class Main
{
    static public function main():Void
    {
        var cat = new Process('cat');
        cat.stdin.writeString('Text to stdout\n');
        trace(cat.stdout.readLine());
        cat = new Process('cat 1>&2');
        cat.stdin.writeString('Text to stderr\n');
        trace(cat.stderr.readLine());
    }
}

Previously, when running with the profiler hl --profile 1000 test.hl the test program fails with the exception:

Uncaught exception: Eof
Called from haxe.io.Input.readLine(.../haxe-4.3.3-linux64/haxe_20231117191750_de28889/std/haxe/io/Input.hx:189)
Called from $Main.main(Main.hx:9)
Called from .init(?:1)

With the proposed changes the test program runs normally and can be profiled.