[ios] generate iOS wrapper into root_out_dir

additional compile targets cause tests that use the test template
in test.gni to generate more than once, making ninja unhappy as
there are multiple rules that generate the script. The underlying
test wrapper was using root_build_dir. Swapping to root_out_dir

Bug: 1063028
Change-Id: I4dffec31bd366ae6811307bae1acd5046d10ea97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2109463
Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751728}

build/config/ios/ios_test_runner_wrapper.gni

@@ -118,7 +118,12 @@ template("ios_test_runner_wrapper") {
     } else {
       _wrapper_output_name = wrapper_output_name
     }
-    wrapper_script = "${root_build_dir}/bin/${_wrapper_output_name}"
+
+    # Test targets may attempt to generate multiple wrappers for a suite with
+    # multiple different toolchains when running with additional_target_cpus.
+    # Generate the wrapper script into root_out_dir rather than root_build_dir
+    # to ensure those wrappers are distinct.
+    wrapper_script = "${root_out_dir}/bin/${_wrapper_output_name}"
 
     # ios/build/bot/scripts/*.py needs to be present for test runner
     if (!defined(data)) {