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='2020-01-16 23:14:05 +0100'>2020-01-16</span></td><td><a href='/guix/commit/tests/cran.scm?id=cfd1ed84013df85f0e473884ef4038b4bd7120d4'>import: cran: Avoid uses of '@@' in the tests.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/import/cran.scm (description-&gt;alist, description-&gt;package): Export.
&lt;top level&gt;: Set! 'listify'.
* tests/cran.scm (description-alist, "description-&gt;package"): Remove use
of '@@' to access the relevant bindings.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-05-13 12:40:20 +0200'>2017-05-13</span></td><td><a href='/guix/commit/tests/cran.scm?id=db427602d8f993ee0025fa68d1af274aa8d69ab9'>import: cran: Robustify cran-package?.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/import/cran.scm (package-&gt;upstream-name): Return #f if url
  start and end index could not be determined.
  (cran-package?): Check if the upstream-name can be extracted from
  given package.
* tests/cran.scm: Add "r-minimal is not a cran package" to make sure that
  r-minimal is not detected as a cran package.

This fixes a failure of guix refresh on r-minimal because no
upsteam-name can be determined from ".../R-version.tar.gz" uri.
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2017-03-08 23:42:52 +0100'>2017-03-08</span></td><td><a href='/guix/commit/tests/cran.scm?id=dd420bf3430eb644b93ca224da4c0a3f5db7a42f'>tests: Avoid zero-expression 'begin' form.</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/cran.scm ("description-&gt;package"): Add body after the expected
pattern in 'match'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-11-10 11:58:43 +0100'>2016-11-10</span></td><td><a href='/guix/commit/tests/cran.scm?id=324a2ba56c2f4c0d91567ed08024ae2c492f3b23'>tests: Adjust 'url-fetch' mocks to TLS changes.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to bc3c41ce36349ed4ec758c70b48a7059e363043a.

* tests/cpan.scm ("cpan-&gt;guix-package"): Add #:verify-certificate?
parameter in 'url-fetch' mock.
* tests/cran.scm ("description-&gt;package"): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>