ntp: fix build w/glibc-2.34

Failing Hydra build: https://hydra.nixos.org/build/155170191

Patch derived from linuxfromscratch/openembedded.org[1][2].

[1] https://www.linuxfromscratch.org/blfs/view/svn/basicnet/ntp.html
[2] https://patchwork.openembedded.org/patch/180019/

pkgs/tools/networking/ntp/default.nix

@@ -9,6 +9,11 @@ stdenv.mkDerivation rec {
     sha256 = "06cwhimm71safmwvp6nhxp6hvxsg62whnbgbgiflsqb8mgg40n7n";
   };
 
+  patches = [
+    # From https://patchwork.openembedded.org/patch/180019/
+    ./glibc-2.34-fix.patch
+  ];
+
   configureFlags = [
     "--sysconfdir=/etc"
     "--localstatedir=/var"

pkgs/tools/networking/ntp/glibc-2.34-fix.patch

@@ -0,0 +1,28 @@
+From 082a504cfcc046c3d8adaae1164268bc94e5108a Mon Sep 17 00:00:00 2001
+From: Khem Raj <raj.khem@gmail.com>
+Date: Sat, 31 Jul 2021 10:51:41 -0700
+Subject: [PATCH] libntp: Do not use PTHREAD_STACK_MIN on glibc
+In glibc 2.34+ PTHREAD_STACK_MIN is not a compile-time constant which
+could mean different stack sizes at runtime on different architectures
+and it also causes compile failure. Default glibc thread stack size
+or 64Kb set by ntp should be good in glibc these days.
+Upstream-Status: Pending
+Signed-off-by: Khem Raj <raj.khem@gmail.com>
+---
+ libntp/work_thread.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+diff --git a/libntp/work_thread.c b/libntp/work_thread.c
+index 03a5647..3ddd751 100644
+--- a/libntp/work_thread.c
++++ b/libntp/work_thread.c
+@@ -41,7 +41,7 @@
+ #ifndef THREAD_MINSTACKSIZE
+ # define THREAD_MINSTACKSIZE	(64U * 1024)
+ #endif
+-#ifndef __sun
++#if !defined(__sun) && !defined(__GLIBC__)
+ #if defined(PTHREAD_STACK_MIN) && THREAD_MINSTACKSIZE < PTHREAD_STACK_MIN
+ # undef THREAD_MINSTACKSIZE
+ # define THREAD_MINSTACKSIZE PTHREAD_STACK_MIN
+-- 
+2.32.0