[libc++][CI] Switches to clang-format-16.

Uses an absolute path to the selected binary.
Updates the formatting of two files to match clang-format-16 style.

Depends on D144126

Reviewed By: #libc, philnik

Differential Revision: https://reviews.llvm.org/D144132

Author: mordante

libcxx/include/__expected/unexpected.h

@@ -64,8 +64,8 @@ class unexpected {
   _LIBCPP_HIDE_FROM_ABI constexpr unexpected(unexpected&&)      = default;
 
   template <class _Error = _Err>
-    requires(!is_same_v<remove_cvref_t<_Error>, unexpected> && //
-             !is_same_v<remove_cvref_t<_Error>, in_place_t> && //
+    requires(!is_same_v<remove_cvref_t<_Error>, unexpected> &&          //
+             !is_same_v<remove_cvref_t<_Error>, in_place_t> &&          //
              is_constructible_v<_Err, _Error>)
   _LIBCPP_HIDE_FROM_ABI constexpr explicit unexpected(_Error&& __error) //
       noexcept(is_nothrow_constructible_v<_Err, _Error>)                // strengthened

libcxx/src/memory_resource.cpp

@@ -107,7 +107,7 @@ static memory_resource* __default_memory_resource(bool set = false, memory_resou
     new_res = new_res ? new_res : new_delete_resource();
     lock_guard<mutex> guard(res_lock);
     memory_resource* old_res = res;
-    res = new_res;
+    res                      = new_res;
     return old_res;
   } else {
     lock_guard<mutex> guard(res_lock);

libcxx/utils/ci/buildkite-pipeline.yml

@@ -56,9 +56,7 @@ steps:
     env:
         CC: "clang-${LLVM_HEAD_VERSION}"
         CXX: "clang++-${LLVM_HEAD_VERSION}"
-        # TODO ENABLE
-        # CLANG_FORMAT: "/usr/bin/clang-format-${LLVM_STABLE_VERSION}"
-        CLANG_FORMAT: "clang-format-15"
+        CLANG_FORMAT: "/usr/bin/clang-format-${LLVM_STABLE_VERSION}"
     agents:
       queue: "libcxx-builders"
       os: "linux"

libcxx/utils/data/ignore_format.txt

@@ -260,7 +260,6 @@ libcxx/include/__chrono/literals.h
 libcxx/include/__chrono/monthday.h
 libcxx/include/__chrono/month.h
 libcxx/include/__chrono/month_weekday.h
-libcxx/include/__chrono/statically_widen.h
 libcxx/include/__chrono/steady_clock.h
 libcxx/include/__chrono/system_clock.h
 libcxx/include/__chrono/time_point.h