Provide a 'mach_print' symbol in libc.

--- a/sysdeps/mach/hurd/i386/libc.abilist	2020-04-01 19:22:44.710088821 +0200
+++ b/sysdeps/mach/hurd/i386/libc.abilist	2020-04-01 19:22:52.062051161 +0200
@@ -338,6 +338,7 @@
 GLIBC_2.2.6 __mach_port_allocate F
 GLIBC_2.2.6 __mach_port_deallocate F
 GLIBC_2.2.6 __mach_port_insert_right F
+GLIBC_2.21 __mach_print F
 GLIBC_2.2.6 __mach_reply_port F
 GLIBC_2.2.6 __mach_task_self_ D 0x4
 GLIBC_2.2.6 __mach_thread_self F

--- a/mach/Versions
+++ b/mach/Versions
@@ -56,6 +56,7 @@
   }
   GLIBC_2.21 {
     __mach_host_self_;
+    mach_print;
   }
 
   HURD_CTHREADS_0.3 {
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<tr><td><span title='2020-11-07 13:19:25 +0100'>2020-11-07</span></td><td><a href='/guix/commit/gnu/installer/newt/ethernet.scm?id=8338d414b361e4fb961221642c1064e9dc89ba65'>installer: Limit listbox height.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes: &lt;https://issues.guix.gnu.org/44428&gt;.

* gnu/installer/newt.scm (init): Print screen size.
* gnu/installer/newt/page.scm (default-listbox-height): New variable.
(run-listbox-selection-page): Use it.
* gnu/installer/newt/wifi.scm (wifi-listbox-height): Ditto.
* gnu/installer/newt/network.scm (run-technology-page): Set the maximum
listbox height to 5.
* gnu/installer/newt/ethernet.scm (run-ethernet-page): Ditto.
* gnu/installer/newt/final.scm (run-config-display-page): Change listbox
height.
* gnu/installer/newt/partition.scm (run-disk-page): Ditto.
* gnu/installer/newt/welcome.scm (display-logo?): New procedure.
(run-menu-page): Use it.
* gnu/installer/steps.scm (%configuration-file-width): Remove it.
</span></span></td><td>Mathieu Othacehe</td></tr>