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;
>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
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<tr><td><span title='2019-04-24 22:21:35 +0200'>2019-04-24</span></td><td><a href='/guix/commit/gnu/services/authentication.scm?id=9374cbd1fb29395a5e849e95e8a249e5f9f944c0'>services: fprintd: Provide polkit policy.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/authentication.scm (fprintd-service-type)[extensions]: Add
polkit-service-type.
</span></span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2019-04-21 10:40:19 +0200'>2019-04-21</span></td><td><a href='/guix/commit/gnu/services/authentication.scm?id=dc01978288318a8155e2e2657be9b278a754ebac'>services: fprintd: Use define-configuration.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/authentication.scm: Use define-configuration in fprintd.
</span></span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2019-04-17 08:51:11 +0200'>2019-04-17</span></td><td><a href='/guix/commit/gnu/services/authentication.scm?id=0682f084635cdc289aabafc4b2583639e00a28b3'>services: fprintd: Fix service.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/authentication.scm (&lt;fprintd-configuration&gt;)[ntp]: Rename to...
[fprintd]: ...this.
(fprintd-dbus-service): New procedure.
(fprintd-service-type): Use it.
[default-value]: Add value.
</span></span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2019-03-20 20:31:15 +0100'>2019-03-20</span></td><td><a href='/guix/commit/gnu/services/authentication.scm?id=c16423f143919916a5273761d7ed29bd49f14519'>services: Add nslcd-service-type.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/authentication.scm (nslcd-service-type, nslcd-configuration,
%nslcd-accounts): New variables.
(uglify-field-name, value-&gt;string, serialize-field, serialize-list,
ssl-option?, tls-reqcert-option?, deref-option?,
comma-separated-list-of-strings?, serialize-ignore-users-option, log-option?,
serialize-log-option, valid-map?, scope-option?, serialize-scope-option,
map-entry?, list-of-map-entries?, filter-entry?, list-of-filter-entries?,
serialize-filter-entry, serialize-list-of-filter-entries, serialize-map-entry,
serialize-list-of-map-entries, nslcd-config-file, nslcd-etc-service,
nslcd-shepherd-service, pam-ldap-pam-services, pam-ldap-pam-service,
generate-nslcd-documentation): New procedures.
* gnu/tests/ldap.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* doc/guix.texi (LDAP Services): Document it.
</span></span></td><td>Ricardo Wurmus</td></tr>