Implement arflags in the GN build.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 3cf72220237662772be19973c54a9c9de54012fd..3ae956acde6dca006455ca12573bd279551ef39f 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -417,6 +417,12 @@ config("compiler") {
       ldflags += [ "-Wl,-plugin-opt,-function-sections" ]
     }
 
+    arflags = [
+      "--plugin",
+      rebase_path("//third_party/llvm-build/Release+Asserts/lib/LLVMgold.so",
+                  root_build_dir),
+    ]

[brucedawson, 2016/04/19 20:59:32]

This arflags initialization is under "if (!is_debug &&
(allow_posix_link_time_opt || is_cfi) && !is_nacl)" whereas before the
equivalent check was under "if ((allow_posix_link_time_opt || is_cfi) &&
invoker.toolchain_os != "nacl")" - the "if (!is_debug" check is new.

Can you confirm that this is intentional or benign?

+
     # TODO(pcc): Make these flags work correctly with CFI.
     if (!is_cfi) {
       cflags += [