Update ReleaseNotes for MC/DC changes. (#95887)

Mostly apparent changes (#82448, #95496) are described here.

clang/docs/ReleaseNotes.rst

@@ -595,6 +595,21 @@ Improvements to Clang's time-trace
 - Clang now specifies that using ``auto`` in a lambda parameter is a C++14 extension when
   appropriate. (`#46059: <https://github.com/llvm/llvm-project/issues/46059>`_).
 
+Improvements to Coverage Mapping
+--------------------------------
+
+- Macros defined in system headers are not expanded in coverage
+  mapping. Conditional expressions in system header macros are no
+  longer taken into account for branch coverage. They can be included
+  with ``-mllvm -system-headers-coverage``.
+  (`#78920: <https://github.com/llvm/llvm-project/issues/78920>`_)
+- MC/DC Coverage has been improved.
+  (`#82448: <https://github.com/llvm/llvm-project/pull/82448>`_)
+
+  - The maximum number of conditions is no longer limited to 6. See
+    `this <SourceBasedCodeCoverage.html#mc-dc-instrumentation>` for
+    more details.
+
 Bug Fixes in This Version
 -------------------------
 - Clang's ``-Wundefined-func-template`` no longer warns on pure virtual

llvm/docs/ReleaseNotes.rst

@@ -70,6 +70,14 @@ Changes to the LLVM IR
   records by default. Details of the change and instructions on how to update
   any downstream tools and tests can be found in the `migration docs
   <https://llvm.org/docs/RemoveDIsDebugInfo.html>`_.
+* Semantics of MC/DC intrinsics have been changed.
+
+  * ``llvm.instprof.mcdc.parameters``: 3rd argument has been changed
+    from bytes to bits.
+  * ``llvm.instprof.mcdc.condbitmap.update``: Removed.
+  * ``llvm.instprof.mcdc.tvbitmap.update``: 3rd argument has been
+    removed. The next argument has been changed from byte index to bit
+    index.
 
 Changes to LLVM infrastructure
 ------------------------------