libbsd: fix build w/musl by adding missing include

Patch from void, with prefix added.

pkgs/development/libraries/libbsd/default.nix

···
   # the configure scripts
   nativeBuildInputs = [ autoreconfHook ];
 
-  patches = stdenv.lib.optional stdenv.isDarwin ./darwin.patch;
+  patches = stdenv.lib.optional stdenv.isDarwin ./darwin.patch
+    # Suitable for all but limited to musl to avoid rebuild
+    ++ stdenv.lib.optional stdenv.hostPlatform.isMusl ./musl.patch;
 
   meta = with stdenv.lib; {
     description = "Common functions found on BSD systems";

pkgs/development/libraries/libbsd/musl.patch

···
+Source: maxice8
+Upstream: no
+Reason: fixes compilation
+
+--- a/src/flopen.c
++++ b/src/flopen.c
+@@ -34,6 +34,7 @@
+ #include <errno.h>
+ #include <stdarg.h>
+ #include <unistd.h>
++#include <fcntl.h>
+ 
+ #include <libutil.h>
+