libbsd: apply upstream patch to fix w/musl

pkgs/development/libraries/libbsd/default.nix

@@ -13,7 +13,10 @@ stdenv.mkDerivation rec {
   # the configure scripts
   nativeBuildInputs = [ autoreconfHook ];
 
-  patches = stdenv.lib.optionals stdenv.isDarwin [ ./darwin.patch ];
+  patches = stdenv.lib.optional stdenv.isDarwin ./darwin.patch
+    # Suitable for all, but limited to musl to avoid rebuilds
+    # https://cgit.freedesktop.org/libbsd/patch/?id=1f8a3f7bccfc84b195218ad0086ebd57049c3490
+    ++ stdenv.lib.optional stdenv.hostPlatform.isMusl ./non-glibc.patch;
 
   meta = with stdenv.lib; {
     description = "Common functions found on BSD systems";

pkgs/development/libraries/libbsd/non-glibc.patch

@@ -0,0 +1,74 @@
+From 1f8a3f7bccfc84b195218ad0086ebd57049c3490 Mon Sep 17 00:00:00 2001
+From: Guillem Jover <guillem@hadrons.org>
+Date: Tue, 6 Mar 2018 01:39:45 +0100
+Subject: Fix function declaration protection for glibc already providing them
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+On non-glibc based systems we cannot unconditionally use the
+__GLIBC_PREREQ macro as it gets expanded before evaluation. Instead,
+if it is undefined, define it to 0.
+
+We should also always declare these functions on non-glibc based
+systems. And on systems with a new enough glibc, which provides these
+functions, we should still provide the declarations if _GNU_SOURCE
+is *not* defined.
+
+Reported-by: Jörg Krause <joerg.krause@embedded.rocks>
+---
+ include/bsd/stdlib.h    | 3 ++-
+ include/bsd/string.h    | 3 ++-
+ include/bsd/sys/cdefs.h | 8 ++++++++
+ 3 files changed, 12 insertions(+), 2 deletions(-)
+
+diff --git a/include/bsd/stdlib.h b/include/bsd/stdlib.h
+index 8d33d1f..a5b063c 100644
+--- a/include/bsd/stdlib.h
++++ b/include/bsd/stdlib.h
+@@ -71,7 +71,8 @@ int sradixsort(const unsigned char **base, int nmemb,
+                const unsigned char *table, unsigned endbyte);
+ 
+ void *reallocf(void *ptr, size_t size);
+-#if defined(_GNU_SOURCE) && defined(__GLIBC__) && !__GLIBC_PREREQ(2, 26)
++#if !defined(__GLIBC__) || \
++    (defined(__GLIBC__) && (!__GLIBC_PREREQ(2, 26) || !defined(_GNU_SOURCE)))
+ void *reallocarray(void *ptr, size_t nmemb, size_t size);
+ #endif
+ 
+diff --git a/include/bsd/string.h b/include/bsd/string.h
+index 29097f6..f987fee 100644
+--- a/include/bsd/string.h
++++ b/include/bsd/string.h
+@@ -46,7 +46,8 @@ size_t strlcat(char *dst, const char *src, size_t siz);
+ char *strnstr(const char *str, const char *find, size_t str_len);
+ void strmode(mode_t mode, char *str);
+ 
+-#if defined(_GNU_SOURCE) && defined(__GLIBC__) && !__GLIBC_PREREQ(2, 25)
++#if !defined(__GLIBC__) || \
++    (defined(__GLIBC__) && (!__GLIBC_PREREQ(2, 25) || !defined(_GNU_SOURCE)))
+ void explicit_bzero(void *buf, size_t len);
+ #endif
+ __END_DECLS
+diff --git a/include/bsd/sys/cdefs.h b/include/bsd/sys/cdefs.h
+index b4c8f30..d1cc419 100644
+--- a/include/bsd/sys/cdefs.h
++++ b/include/bsd/sys/cdefs.h
+@@ -59,6 +59,14 @@
+ #endif
+ 
+ /*
++ * On non-glibc based systems, we cannot unconditionally use the
++ * __GLIBC_PREREQ macro as it gets expanded before evaluation.
++ */
++#ifndef __GLIBC_PREREQ
++#define __GLIBC_PREREQ(maj, min) 0
++#endif
++
++/*
+  * Some kFreeBSD headers expect those macros to be set for sanity checks.
+  */
+ #ifndef _SYS_CDEFS_H_
+-- 
+cgit v1.1
+