Fix CVE-2019-19126:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-19126
https://sourceware.org/bugzilla/show_bug.cgi?id=25204

Taken from upstream:
https://sourceware.org/git/?p=glibc.git;a=commit;h=37c90e117310728a4ad1eb998c0bbe7d79c4a398

diff --git a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
index 975cbe2..df2cdfd 100644
--- a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
+++ b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
@@ -31,7 +31,8 @@
    environment variable, LD_PREFER_MAP_32BIT_EXEC.  */
 #define EXTRA_LD_ENVVARS \
   case 21:								  \
-    if (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0)		  \
+    if (!__libc_enable_secure						  \
+	&& memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0)		  \
       GLRO(dl_x86_cpu_features).feature[index_arch_Prefer_MAP_32BIT_EXEC] \
 	|= bit_arch_Prefer_MAP_32BIT_EXEC;				  \
     break;
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<tr><td><span title='2020-05-08 16:30:50 +0200'>2020-05-08</span></td><td><a href='/guix/commit/gnu/system/pam.scm?id=dd0804c67e99914eecc471fdb92f4220425a1cbc'>services: Add descriptions.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/dbus.scm (polkit-service-type)[description]: New field.
* gnu/services/dict.scm (dicod-service-type)[description]: New field.
* gnu/services/dns.scm (knot-service-type)[description]: New field.
* gnu/services/networking.scm (dhcpd-service-type)[description]: New field.
* gnu/services/shepherd.scm (shepherd-root-service-type)[description]:
New field.
* gnu/services/xorg.scm (slim-service-type)[description]: New field.
(screen-locker-service-type)[description]: New field.
* gnu/system/pam.scm (pam-root-service-type)[description]: New field.
* gnu/system/shadow.scm (account-service-type)[description]: New field.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-05-09 12:11:36 +0200'>2019-05-09</span></td><td><a href='/guix/commit/gnu/system/pam.scm?id=af55ca481d9e6c1d1e06632f96d550b42f33210f'>system: pam: Add #:login-uid? parameter to 'unix-pam-service'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/pam.scm (unix-pam-service): Add #:login-uid? parameter.  In
then 'session' field, add "pam_loginuid.so" as required when LOGIN-UID?
is true.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-09-22 00:05:08 +0200'>2017-09-22</span></td><td><a href='/guix/commit/gnu/system/pam.scm?id=fbc31dc1247d3a494246e69f3cf28476af9eb9d6'>services: Move 'session-environment-service-type' to pam.scm.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/base.scm (environment-variables-&gt;environment-file)
(session-environment-service-type)
(session-environment-service): Move to...
* gnu/system/pam.scm: ... here.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-05-08 23:11:01 +0200'>2017-05-08</span></td><td><a href='/guix/commit/gnu/system/pam.scm?id=e586257b550918fefaab3970f2c314d6285f54ab'>system: Allow root to run "su" without password.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/pam.scm (unix-pam-service): Add pam-entry for "pam_rootok.so" to
auth field when ALLOW-ROOT? is #T.
(base-pam-services): Allow root to run "su" without authentication.
</span></span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2016-11-06 19:56:43 +0100'>2016-11-06</span></td><td><a href='/guix/commit/gnu/system/pam.scm?id=290ad2243c0ce2919918f64fec5652b5a60466a8'>gnu: Remove comment which is factually incorrect.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/system/pam.scm: Remove incorrect comment.
</span></span></td><td>John Darrington</td></tr>