ios: Support building with Xcode 27

Add support for building iOS targets with Xcode 27:

- Add _Builtin_float dependency to _DarwinFoundation1 module in
  buildtools/third_party/libc++/BUILD.gn. Xcode 27's math.h includes
  float.h when modules are enabled, which requires _Builtin_float in
  explicit module builds.
- Ignore CoreAudioTypes auto-linked framework option globally in
  build/config/ios/BUILD.gn under LLD. Xcode 27 auto-links this
  header-only framework (which lacks a binary), causing LLD to fail.
- Remove the redundant local CoreAudioTypes ignore flag in
  ios/chrome/app/chrome_app.gni.

Change-Id: Ia03a9da205754591442355f99fa42e21e05ed0dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7910583
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Auto-Submit: Justin Cohen <justincohen@google.com>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1643921}
NOKEYCHECK=True
GitOrigin-RevId: 99cfba998c72a38723c5cfb791c53c2533969842