Unbreak mac component build.

mojo/public/cpp/system/BUILD.gn

Index: mojo/public/cpp/system/BUILD.gn
diff --git a/mojo/public/cpp/system/BUILD.gn b/mojo/public/cpp/system/BUILD.gn
index 7830d251d5ebe7b97aa8f522d2473e8f5c563ed9..0dc7af9d4d7b907176b6da3891fb3f48fd8510dc 100644
--- a/mojo/public/cpp/system/BUILD.gn
+++ b/mojo/public/cpp/system/BUILD.gn
@@ -2,7 +2,26 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# Deletes libsystem.dylib from the build dir, since it shadows
+# /usr/lib/libSystem.dylib on macOS.
+# TODO(thakis): Remove this after a while.
+action("clean_up_old_dylib") {
+  script = "//build/rm.py"
+  stamp = "$target_gen_dir/clean_up_stamp"
+  outputs = [
+    stamp,
+  ]
+  args = [
+    "--stamp",
+    rebase_path(stamp, root_build_dir),
+    "-f",
+    "libsystem.dylib",
+  ]
+}
+
 component("system") {
+  output_name = "mojo_public_system_cpp"
+
   sources = [
     "buffer.cc",
     "buffer.h",
@@ -23,6 +42,9 @@ component("system") {
     "//base",
     "//mojo/public/c/system",
   ]
+  deps = [
+    ":clean_up_old_dylib",
+  ]
 
   defines = [ "MOJO_CPP_SYSTEM_IMPLEMENTATION" ]
 }