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;
ass='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
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<tr><td><span title='2019-11-09 23:04:14 +0100'>2019-11-09</span></td><td><a href='/guix/commit/gnu/tests/singularity.scm?id=f0034427f50be1bcab137d9877c3586e4be4d83e'>tests: Update references to the now-deprecated 'guile-json' variable.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/tests/docker.scm (build-tarball&amp;run-docker-test): Refer to
'guile-json-3' instead of 'guile-json'.
* gnu/tests/singularity.scm (build-tarball&amp;run-singularity-test):
Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-07-04 18:05:02 +0200'>2019-07-04</span></td><td><a href='/guix/commit/gnu/tests/singularity.scm?id=dea62932bc929243dae5e8b08f4fbe0b6f70be95'>pack: 'squashfs' backend records the profile's search paths.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/pack.scm (singularity-environment-file): New procedure.
(squashfs-image): Use it, and create /.singularity/env/90-environment.sh.
* gnu/tests/singularity.scm (run-singularity-test)["singularity run,
with environment"]: New test, currently skipped.
* gnu/tests/singularity.scm (build-tarball&amp;run-singularity-test): Add
GUILE-JSON to the profile.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-06-07 09:57:19 +0200'>2019-06-07</span></td><td><a href='/guix/commit/gnu/tests/singularity.scm?id=a0f352b30f4869a7af7017b8a5011ac7602dd115'>pack: Add '--entry-point'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/pack.scm (self-contained-tarball): Add #:entry-point and
warn when it's true.
(squashfs-image): Add #:entry-point and honor it.
(docker-image): Add #:entry-point and honor it.
(%options, show-help): Add '--entry-point'.
(guix-pack): Honor '--entry-point' and pass #:entry-point to BUILD-IMAGE.
* gnu/tests/docker.scm (run-docker-test): Test 'docker run' with the
default entry point.
(build-tarball&amp;run-docker-test): Pass #:entry-point to 'docker-image'.
* doc/guix.texi (Invoking guix pack): Document it.
* gnu/tests/singularity.scm (run-singularity-test)["singularity run"]:
New test.
(build-tarball&amp;run-singularity-test): Pass #:entry-point to
'squashfs-image'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-06-07 09:57:19 +0200'>2019-06-07</span></td><td><a href='/guix/commit/gnu/tests/singularity.scm?id=08814aec6ae75adcd059c5235c90ad26e5d5607e'>services: Add Singularity.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/linux.scm (singularity)[source](snippet): Change file
name of setuid helpers in libexec/cli/*.exec.
[arguments]: Remove "--disable-suid".
* gnu/services/docker.scm (%singularity-activation): New variable.
(singularity-setuid-programs): New procedure.
(singularity-service-type): New variable.
* gnu/tests/singularity.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* doc/guix.texi (Miscellaneous Services): Document it.
</span></span></td><td>Ludovic Courtès</td></tr>