elfutils: Respect $NIX_DEBUG_INFO_DIRS

Look up .build-id files relative to the directories in the

colon-separated environment variable NIX_DEBUG_INFO_DIRS, unless

overriden by --debuginfo-path.

diff -ru elfutils-0.169-orig/libdwfl/argp-std.c elfutils-0.169/libdwfl/argp-std.c

--- elfutils-0.169-orig/libdwfl/argp-std.c	2017-05-02 23:05:52.000000000 +0200

+++ elfutils-0.169/libdwfl/argp-std.c	2017-07-28 16:08:06.739558106 +0200

@@ -376,5 +376,7 @@

 const struct argp *

 dwfl_standard_argp (void)

 {

+  debuginfo_path = getenv("NIX_DEBUG_INFO_DIRS");

+

   return &libdwfl_argp;

 }

diff -ru elfutils-0.169-orig/src/stack.c elfutils-0.169/src/stack.c

--- elfutils-0.169-orig/src/stack.c	2017-02-24 11:55:28.000000000 +0100

+++ elfutils-0.169/src/stack.c	2017-07-28 15:50:06.743196696 +0200

@@ -631,6 +631,8 @@

   /* Set locale.  */

   (void) setlocale (LC_ALL, "");

+  debuginfo_path = getenv("NIX_DEBUG_INFO_DIRS");

+

   const struct argp_option options[] =

     {

       { NULL, 0, NULL, 0, N_("Input selection options:"), 0 },

{ lib, stdenv, fetchurl, m4, zlib, bzip2, bison, flex, gettext, xz }:

{ lib, stdenv, fetchurl, m4, zlib, bzip2, bison, flex, gettext, xz, setupDebugInfoDirs }:

# TODO: Look at the hardcoded paths to kernel, modules etc.

stdenv.mkDerivation rec {

    sha256 = "1hiv1yqig3292dwqhrwsxwk3qjalxp5fpl8yphwbfwh8ng3zl4ll";

  };

  patches = ./debug-info-from-env.patch;

  hardeningDisable = [ "format" ];

  # We need bzip2 in NativeInputs because otherwise we can't unpack the src,

  nativeBuildInputs = [ m4 bison flex gettext bzip2 ];

  buildInputs = [ zlib bzip2 xz ];

  propagatedNativeBuildInputs = [ setupDebugInfoDirs ];

  configureFlags =

    [ "--program-prefix=eu-" # prevent collisions with binutils

      "--enable-deterministic-archives"