Adding Compiler configs to iOS.

BUG=459705

Review URL: https://codereview.chromium.org/1343403002

Cr-Original-Commit-Position: refs/heads/master@{#349482}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a1b18778642e62768180ba000ed60dcb5feca8e9

config/BUILDCONFIG.gn

@@ -382,6 +382,7 @@ if (is_linux) {
 } else if (is_mac) {
   _native_compiler_configs += [ "//build/config/mac:sdk" ]
 } else if (is_ios) {
+  _native_compiler_configs += [ "//build/config/ios:sdk" ]
 } else if (is_android) {
   _native_compiler_configs += [ "//build/config/android:sdk" ]
 }