[libc++][NFC] Reorganize release notes

Several entries were in the wrong place, such as API changes appearing
under "Build System Changes". This commit shuffles stuff so it sits under
the right section.

diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
index 7d116e5..8d01a49 100644 (file)
--- a/libcxx/docs/ReleaseNotes.rst
+++ b/libcxx/docs/ReleaseNotes.rst
@@ -42,23 +42,17 @@ New Features
   is incomplete. Some functions are known to be inefficient; both in memory
   usage and performance. The implementation is considered experimental and isn't
   considered ABI stable.
+
 - There's a new CMake option ``LIBCXX_ENABLE_UNICODE`` to disable Unicode
   support in the ``<format>`` header. This only affects the estimation of the
   output width of the format functions.
 
-API Changes
------------
-
 - Support for building libc++ on top of a C Standard Library that does not support ``wchar_t`` was
   added. This is useful for building libc++ in an embedded setting, and it adds itself to the various
   freestanding-friendly options provided by libc++.
 
-Build System Changes
---------------------
-
-- Building the libc++ shared or static library requires a C++ 20 capable compiler.
-  Consider using a Bootstrapping build to build libc++ with a fresh Clang if you
-  can't use the system compiler to build libc++ anymore.
+API Changes
+-----------
 
 - The functions ``std::atomic<T*>::fetch_(add|sub)`` and
   ``std::atomic_fetch_(add|sub)`` no longer accept a function pointer. While
@@ -78,6 +72,13 @@ Build System Changes
   Calls to these functions where the template argument was deduced by the
   compiler are unaffected by this change.
 
+Build System Changes
+--------------------
+
+- Building the libc++ shared or static library requires a C++ 20 capable compiler.
+  Consider using a Bootstrapping build to build libc++ with a fresh Clang if you
+  can't use the system compiler to build libc++ anymore.
+
 - Historically, there has been numerous ways of building libc++ and libc++abi. This has
   culminated in over 5 different ways to build the runtimes, which made it impossible to
   maintain with a good level of support. Starting with this release, the runtimes support