Add third_party/elfutils:libelf to the gn build.

BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 51 matching lines @@
     "//skia",
     "//storage/browser",
     "//sql",
     "//sync",
     "//third_party/WebKit/public:all_blink",
     "//third_party/angle:translator",
     "//third_party/brotli",
     "//third_party/cacheinvalidation",
     "//third_party/cld",
     "//third_party/cld_2",
+    "//third_party/elfutils:libelf($host_toolchain)",

[brettw, 2014/10/10 17:48:04]

We only want to build this for desktop Linux, which means it probably shouldn't
be in this list. I suspect that this target is one that should only be brought
in "organically" when something else depends on it rather than always being
built. Is something like that coming in a followup?

[simonb (inactive), 2014/10/10 18:00:47]

Gone, then (though this makes it awkward to test with gn gen ...).

The thing that depends on this -- tools/relocation_packer -- doesn't yet build
with gn, but when I have that working then yes, libelf will be drawn in to the
host build via dependencies.

     "//third_party/ffmpeg",
     "//third_party/flac",
     "//third_party/harfbuzz-ng",
     "//third_party/hunspell",
     "//third_party/iccjpeg",
     "//third_party/icu",
     "//third_party/leveldatabase",
     "//third_party/libphonenumber",
     "//third_party/libjingle",
     "//third_party/libpng",
@@ skipping 146 matching lines @@
     ]
   }
 
   # Non-mobile builds.
   if (!is_android && !is_ios) {
     deps += [
       "//device/usb",
     ]
   }
 }