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='2021-02-22 12:07:45 +0100'>2021-02-22</span></td><td><a href='/guix/commit/tests/guix-lint.sh?id=9a38bed2cf32e9462badfa43e74cdd4580e804fc'>packages: 'package-field-location' handles 'search-path' returning #f.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/46390&gt;.
Reported by zimoun &lt;zimon.toutoune@gmail.com&gt;.

This is similar to the fix in d10474c38d58bdc676e64336769dc2e00cdfa8ed.

* guix/packages.scm (package-field-location): Handle FILE not in %LOAD-PATH.
* tests/guix-lint.sh: Add test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-28 21:06:36 -0500'>2020-09-28</span></td><td><a href='/guix/commit/tests/guix-lint.sh?id=d8934360d2453a403b5433e71d09188e4ed23b57'>tests: Simplify shell exit status negation;</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/guix-archive.sh, tests/guix-build-branch.sh, tests/guix-build.sh,
tests/guix-daemon.sh, tests/guix-download.sh, tests/guix-environment.sh,
tests/guix-gc.sh, tests/guix-git-authenticate.sh, tests/guix-graph.sh,
tests/guix-hash.sh, tests/guix-lint.sh, tests/guix-pack-relocatable.sh,
tests/guix-pack.sh, tests/guix-package-aliases.sh, tests/guix-package-net.sh,
tests/guix-package.sh: Use the shell '!' keyword to negate command exit status
in place of 'if ...; then false; else true; fi'
</span></span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2020-08-23 23:05:16 +0200'>2020-08-23</span></td><td><a href='/guix/commit/tests/guix-lint.sh?id=d10474c38d58bdc676e64336769dc2e00cdfa8ed'>lint: formatting: Gracefully handle relative file names.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/42543&gt;.
Reported by Jack Hill &lt;jackhill@jackhill.us&gt;.

* guix/lint.scm (check-formatting): Always return a list (previously we
would return #f when 'search-path' returns #f).  Check whether
LOCATION's file is a relative file name.  Return a warning if not.
* tests/guix-lint.sh: Add test.
</span></span></td><td>Ludovic Courtès</td></tr>