This patch reinstates fallback code when the 'prlimit64' system call is
missing by reverting the relevant part of this upstream commit:

  commit 695d7d138eda449678a1650a8b8b58181033353f
  Author: Joseph Myers <joseph@codesourcery.com>
  Date:   Tue May 9 14:05:09 2017 +0000

      Assume prlimit64 is available.

The fallback code is useful on systems that lack 'prlimit64', such as the
2.6.32-on-steroid kernel found on RHEL 6:

  <https://lists.gnu.org/archive/html/guix-devel/2018-03/msg00349.html>

diff --git a/sysdeps/unix/sysv/linux/getrlimit64.c b/sysdeps/unix/sysv/linux/getrlimit64.c
index 37c173286f..56af3c0646 100644
--- b/sysdeps/unix/sysv/linux/getrlimit64.c
+++ a/sysdeps/unix/sysv/linux/getrlimit64.c
@@ -35,7 +35,40 @@
 int
 __getrlimit64 (enum __rlimit_resource resource, struct rlimit64 *rlimits)
 {
-  return INLINE_SYSCALL_CALL (prlimit64, 0, resource, NULL, rlimits);
+#ifdef __NR_prlimit64
+  int res = INLINE_SYSCALL_CALL (prlimit64, 0, resource, NULL, rlimits)</td></tr></table>
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