Revert "libyuv: Include foo_posix.cc in the gn build, like it's done in the gyp build."

BUG=496928
R=thakis@chromium.org

Review URL: https://webrtc-codereview.appspot.com/58399004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1424 16f28f9a-4ce2-e073-06de-1de4eb20be90

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index ff38a05..a240d11 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -17,12 +17,7 @@
 
 use_neon = current_cpu == "arm" && (arm_use_neon || arm_optionally_use_neon)
 
-static_library("libyuv") {
-  # libyuv requires that foo_posix.cc is linked in on Windows too,
-  # just like in libyuv.gyp
-  # TODO(thakis): Fix this, http://crbug.com/496928
-  set_sources_assignment_filter([])
-
+source_set("libyuv") {
   sources = [
     "include/libyuv.h",
     "include/libyuv/basic_types.h",