[ios] Default use_xcode_clang to false for all builders.

Bug: 964650
Change-Id: I23109e8e3dbcacfe4a24611f5a3d5de29708a156
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1650236
Reviewed-by: Misha Efimov <mef@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#667733}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 0fc28f5201e13086c79e5b3fe8d7671afec78c1b
diff --git a/toolchain.gni b/toolchain.gni
index 9a13d29..5101f6e 100644
--- a/toolchain.gni
+++ b/toolchain.gni
@@ -18,9 +18,9 @@
   llvm_force_head_revision = false
   # Compile with Xcode version of clang instead of hermetic version shipped
-  # with the build. Used on iOS to ship official builds (as they are built
-  # with the version of clang shipped with Xcode).
-  use_xcode_clang = is_ios && is_official_build
+  # with the build. Used to be used iOS for official builds, but is now off by
+  # default for all configurations.
+  use_xcode_clang = false
   # Used for binary size analysis.
   generate_linker_map = is_android && is_official_build