gnu: guile: Fix 'posix_spawn' usage for GNU/Hurd.

* gnu/packages/guile.scm (guile-3.0)[arguments]: Add
'patch-posix-spawn-usage' phase.
* gnu/packages/patches/guile-hurd-posix-spawn.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/packages/patches/guile-hurd-posix-spawn.patch

@@ -0,0 +1,44 @@
+Fix <https://issues.guix.gnu.org/61095>, which affects GNU/Hurd.
+
+diff --git a/libguile/posix.c b/libguile/posix.c
+index 3a8be94e4..f5fdc544c 100644
+--- a/libguile/posix.c
++++ b/libguile/posix.c
+@@ -1326,7 +1326,14 @@ static void
+ close_inherited_fds_slow (posix_spawn_file_actions_t *actions, int max_fd)
+ {
+   while (--max_fd > 2)
+-    posix_spawn_file_actions_addclose (actions, max_fd);
++    {
++      /* Adding invalid file descriptors to an 'addclose' action leads
++         to 'posix_spawn' failures on some operating systems:
++         <https://bugs.gnu.org/61095>.  Hence the extra check.  */
++      int flags = fcntl (max_fd, F_GETFD, NULL);
++      if ((flags >= 0) && ((flags & FD_CLOEXEC) == 0))
++        posix_spawn_file_actions_addclose (actions, max_fd);
++    }
+ }
+ 
+ static void
+
+Fix <https://issues.guix.gnu.org/62501>.
+
+diff --git a/test-suite/tests/posix.test b/test-suite/tests/posix.test
+index f20e04453..d5cf47cda 100644
+--- a/test-suite/tests/posix.test
++++ b/test-suite/tests/posix.test
+@@ -431,7 +431,13 @@
+       (let ((str (get-string-all (car input+output))))
+         (close-port (car input+output))
+         (waitpid pid)
+-        str)))
++
++        ;; On GNU/Hurd, the exec server prepends 'LD_ORIGIN_PATH' for
++        ;; every program: <https://bugs.gnu.org/62501>.  Strip it.
++        (if (and (string=? "GNU" (utsname:sysname (uname)))
++                 (string-prefix? "LD_ORIGIN_PATH=" str))
++            (string-drop str (+ 1 (string-index str #\newline)))
++            str))))
+ 
+   (pass-if-equal "ls /proc/self/fd"
+       "0\n1\n2\n3\n"                     ;fourth FD is for /proc/self/fd