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;
   }
 
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<div class='path'>path: <a href='/guix/log/?id=c526b3176fb85175ea0d3a5b561927a23522263b'>root</a>/<a href='/guix/log/tests?id=c526b3176fb85175ea0d3a5b561927a23522263b'>tests</a>/<a href='/guix/log/tests/accounts.scm?id=c526b3176fb85175ea0d3a5b561927a23522263b'>accounts.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/accounts.scm?id=c526b3176fb85175ea0d3a5b561927a23522263b&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-04-27 16:30:40 +0200'>2019-04-27</span></td><td><a href='/guix/commit/tests/accounts.scm?id=0c329bf4b0c00abdc9a7d9c818d36d4d60b3005d'>tests: Adjust accounts test to shell-as-config change.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 504a0fc636ec591e65b4a229a37e522e425d8a0c.

* tests/accounts.scm ("allocate-passwd with previous state"): Change
expected 'shell' for "alice" to "/bin/sh".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-25 23:37:06 +0100'>2019-03-25</span></td><td><a href='/guix/commit/tests/accounts.scm?id=cf848cc0a17a3a58d600116896f6e7abfb0440d4'>accounts: Add default value for the 'home-directory' field of &lt;user-account&gt;.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/accounts.scm (&lt;user-account&gt;)[home-directory]: Mark as
thunked and add a default value.
(default-home-directory): New procedure.
* doc/guix.texi (User Accounts): Remove 'home-directory' from example.
* gnu/system/examples/bare-bones.tmpl: Likewise.
* gnu/system/examples/beaglebone-black.tmpl: Likewise.
* gnu/system/examples/desktop.tmpl: Likewise.
* gnu/system/examples/docker-image.tmpl: Likewise.
* gnu/system/examples/lightweight-desktop.tmpl: Likewise.
* gnu/system/install.scm (installation-os): Likewise.
* gnu/tests.scm (%simple-os): Likewise.
* gnu/tests/install.scm (%minimal-os, %minimal-os-on-vda):
(%separate-home-os, %encrypted-root-os, %btrfs-root-os): Likewise.
* tests/accounts.scm ("allocate-passwd")
("allocate-passwd with previous state"): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-07 20:05:09 +0100'>2019-03-07</span></td><td><a href='/guix/commit/tests/accounts.scm?id=ec600e4544729f1aaf46fa5162bba334515d0de5'>Add (gnu build accounts).</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/build/accounts.scm, tests/accounts.scm: New files.
* Makefile.am (SCM_TESTS): Add tests/accounts.scm.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add build/accounts.scm.
</span></span></td><td>Ludovic Courtès</td></tr>