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='2021-06-13 20:46:01 +0200'>2021-06-13</span></td><td><a href='/guix/commit/bootstrap?id=bd02e50a02ceed914135dba1e69e4457e489cf86'>bootstrap: Simplify search for translation languages.</a><span class='msg-avail'>...<span class='msg-tooltip'>Extend the sed script to also behave like "basename",
saving the addtional call of "xargs basename".

* bootstrap (langs): Extend sed scripts, remove running xargs.
</span></span></td><td>Hartmut Goebel</td></tr>
<tr><td><span title='2020-02-17 11:49:08 +0100'>2020-02-17</span></td><td><a href='/guix/commit/bootstrap?id=3dd311e3a059131ef245417106d4fb659222ef3c'>bootstrap: Fix typo.</a><span class='msg-avail'>...<span class='msg-tooltip'>* bootstrap: Substitute ‘guix-cookbook’ for copy/pasted ‘guix-manual’.

Reported-by: jetomit on #guix
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>