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);
+  if (res == 0 || errno != ENOSYS)
+    return res;
+#endif
+
+/* The fallback code only makes sense if the platform supports either
+   __NR_ugetrlimit and/or __NR_getrlimit.  */
+#if defined (__NR_ugetrlimit) || defined (__NR_getrlimit)
+# ifndef __NR_ugetrlimit
+#  define __NR_ugetrlimit __NR_getrlimit
+# endif
+# if __RLIM_T_MATCHES_RLIM64_T
+#  define rlimits32 (*rlimits)
+# else
+  struct rlimit rlimits32;
+# endif
+
+  if (INLINE_SYSCALL_CALL (ugetrlimit, resource, &rlimits32) < 0)
+    return -1;
+
+# if !__RLIM_T_MATCHES_RLIM64_T
+  if (rlimits32.rlim_cur == RLIM_INFINITY)
+    rlimits->rlim_cur = RLIM64_INFINITY;
+  else
+    rlimits->rlim_cur = rlimits32.rlim_cur;
+  if (rlimits32.rlim_max == RLIM_INFINITY)
+    rlimits->rlim_max = RLIM64_INFINITY;
+  else
+    rlimits->rlim_max = rlimits32.rlim_max;
+# endif /* !__RLIM_T_MATCHES_RLIM64_T */
+#endif /* defined (__NR_ugetrlimit) || defined (__NR_getrlimit)  */
+
+  return 0;
 }
 libc_hidden_def (__getrlimit64)
 
diff --git a/sysdeps/unix/sysv/linux/setrlimit.c b/sysdeps/unix/sysv/linux/setrlimit.c
index 01812ac355..8773c78236 100644
--- b/sysdeps/unix/sysv/linux/setrlimit.c
+++ a/sysdeps/unix/sysv/linux/setrlimit.c
@@ -34,6 +34,7 @@
 int
 __setrlimit (enum __rlimit_resource resource, const struct rlimit *rlim)
 {
+# ifdef __NR_prlimit64
   struct rlimit64 rlim64;
 
   if (rlim->rlim_cur == RLIM_INFINITY)
@@ -45,7 +46,11 @@
   else
     rlim64.rlim_max = rlim->rlim_max;
 
-  return INLINE_SYSCALL_CALL (prlimit64, 0, resource, &rlim64, NULL);
+  int res = INLINE_SYSCALL_CALL (prlimit64, 0, resource, &rlim64, NULL);
+  if (res == 0 || errno != ENOSYS)
+    return res;
+# endif
+  return INLINE_SYSCALL_CALL (setrlimit, resource, rlim);
 }
 
 # if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2)
diff --git a/sysdeps/unix/sysv/linux/setrlimit64.c b/sysdeps/unix/sysv/linux/setrlimit64.c
index 2dd129d99e..db1960fc18 100644
--- b/sysdeps/unix/sysv/linux/setrlimit64.c
+++ a/sysdeps/unix/sysv/linux/setrlimit64.c
@@ -36,7 +36,36 @@
 int
 __setrlimit64 (enum __rlimit_resource resource, const struct rlimit64 *rlimits)
 {
-  return INLINE_SYSCALL_CALL (prlimit64, 0, resource, rlimits, NULL);
+  int res;
+
+#ifdef __NR_prlimit64
+  res = INLINE_SYSCALL_CALL (prlimit64, 0, resource, rlimits, NULL);
+  if (res == 0 || errno != ENOSYS)
+    return res;
+#endif
+
+/* The fallback code only makes sense if the platform supports
+   __NR_setrlimit.  */
+#ifdef __NR_setrlimit
+# if !__RLIM_T_MATCHES_RLIM64_T
+  struct rlimit rlimits32;
+
+  if (rlimits->rlim_cur >= RLIM_INFINITY)
+    rlimits32.rlim_cur = RLIM_INFINITY;
+  else
+    rlimits32.rlim_cur = rlimits->rlim_cur;
+  if (rlimits->rlim_max >= RLIM_INFINITY)
+    rlimits32.rlim_max = RLIM_INFINITY;
+  else
+    rlimits32.rlim_max = rlimits->rlim_max;
+# else
+#  define rlimits32 (*rlimits)
+# endif
+
+  res = INLINE_SYSCALL_CALL (setrlimit, resource, &rlimits32);
+#endif
+
+  return res;
 }
 weak_alias (__setrlimit64, setrlimit64)