httping: pull upstream fix for darwin

Without the change build fails as:

clang -Wall -W -Wextra -pedantic -D_FORTIFY_SOURCE=2 -DVERSION=\"2.9\" -DLOCALEDIR=\"/usr/share/locale\" -DNC -DFW -D_DEBUG -ggdb -c -o nc.o nc.c
In file included from nc.c:22:
./utils.h:19:15: error: unknown type name 'useconds_t'
void myusleep(useconds_t v);
^
make: *** [<builtin>: nc.o] Error 1

Closes: https://github.com/NixOS/nixpkgs/issues/202946

pkgs/tools/networking/httping/default.nix

···
 { lib
 , stdenv
 , fetchFromGitHub
+, fetchpatch
 , fftw ? null
 , gettext
 , libintl
···
     rev = "v${version}";
     hash = "sha256-aExTXXtW03UKMuMjTMx1k/MUpcRMh1PdSPkDGH+Od70=";
   };
+
+  patches = [
+    # Pull upstream fix for missing <unistd.h>
+    #   https://github.com/folkertvanheusden/HTTPing/pull/8
+    (fetchpatch {
+      name = "add-unistd.patch";
+      url = "https://github.com/folkertvanheusden/HTTPing/commit/aad3c275686344fe9a235faeac4ee3832f3aa8d5.patch";
+      hash = "sha256-bz3AMQTSfSTwUyf9WbkAFWVmFo06ei+Qd55x+RRDREY=";
+    })
+  ];
 
   nativeBuildInputs = [
     gettext