[iOS/GN] Allow compilation with system clang.

build/config/sanitizers/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/toolchain.gni")
 
 # Contains the dependencies needed for sanitizers to link into executables and
@@ skipping 52 matching lines @@
       data += [ "$root_out_dir/libc++.so" ]
     }
     if (is_mac) {
       data_deps = [
         ":copy_asan_runtime",
       ]
     }
   }
 }
 
-if (is_mac) {
+if (is_mac && using_sanitizer) {
   copy("copy_asan_runtime") {
     sources = [
       "//third_party/llvm-build/Release+Asserts/lib/clang/$clang_version/lib/darwin/libclang_rt.asan_osx_dynamic.dylib",
     ]
     outputs = [
       "$root_out_dir/{{source_file_part}}",
     ]
   }
 }
 
@@ skipping 345 matching lines @@
 # This allows to selectively disable ubsan_vptr, when needed. In particular,
 # if some third_party code is required to be compiled without rtti, which
 # is a requirement for ubsan_vptr.
 config("default_sanitizer_flags_but_ubsan_vptr") {
   configs = all_sanitizer_configs - [ ":ubsan_vptr_flags" ]
 }
 
 config("default_sanitizer_flags_but_coverage") {
   configs = all_sanitizer_configs - [ ":coverage_flags" ]
 }