GN: Use lib.unstripped rather than lib.stripped. Add a toolchain.gni

mandoline/services/core_services/BUILD.gn

Index: mandoline/services/core_services/BUILD.gn
diff --git a/mandoline/services/core_services/BUILD.gn b/mandoline/services/core_services/BUILD.gn
index cf640e6313da5a9eb5581224575f0303c9f741f2..84f6f2849746c9ac51aa70d73ab3bde2ebd24466 100644
--- a/mandoline/services/core_services/BUILD.gn
+++ b/mandoline/services/core_services/BUILD.gn
@@ -6,6 +6,7 @@
 # we ship with.
 
 import("//build/config/ui.gni")
+import("//build/toolchain/toolchain.gni")
 import("//mojo/public/mojo_application.gni")
 
 mojo_native_application("core_services") {
@@ -17,8 +18,8 @@ mojo_native_application("core_services") {
   if (is_win) {
     copy("copy_files") {
       sources = [
-        "$root_out_dir/libEGL.dll",
-        "$root_out_dir/libGLESv2.dll",
+        "$root_shlib_dir/libEGL.dll",
+        "$root_shlib_dir/libGLESv2.dll",
       ]
       outputs = [
         "$root_out_dir/core_services/{{source_file_part}}",