Subject: Proc open-input-pipe returns #eof when reading on macOS, works as expected on Linux

From: Jose Ortiz <[email-masked]>
Date: Wed, 21 Jun 2023 17:31:18 -0700

When reading from open-input-pipe, it returns #eof on macOS devices, while it works properly in Linux.

```
(use-modules (ice-9 popen)
              (ice-9 rdelim))
(let* ((port (open-input-pipe "date --utc"))
        (str  (read-line port)))
   (close-pipe port)
   str)
```
macOS> #<eof>
linux> "Thu Jun 22 12:30:26 AM UTC 2023"

Building latest and running popen.test also fails with:

m1 :: Projects/guile/test-suite ? guile -L . -e main -s guile-test tests/popen.test
Running tests/popen.test
                                                                                                                                                                   
FAIL: tests/popen.test: open-input-pipe: echo hello
FAIL: tests/popen.test: open-input-pipe: open-input-pipe process gets (current-input-port) as stdin
ERROR: tests/popen.test: open-output-pipe: no duplicate - arguments: ((wrong-type-arg "string-append" "Wro
ng type (expecting ~A): ~S" ("string" #f) (#f)))

- Jose