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='2022-08-11 11:55:19 -0400'>2022-08-11</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=2b579fd4f453bb1a3592eb8e634ea1dff64efab6'>gnu: artwork: Update repository to latest commit.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/artwork.scm (%artwork-repository): Update to commit
4c7f2ce6428a63e202cd2a9474a06f68a946934d.
</span></span></td><td>Maxim Cournoyer</td></tr>