[clang] [docs] Update the changes of C++20 Modules in clang15

Since clang15 is going to be branched in July 26, and C++ modules still
lack an update on ReleaseNotes. Although it is not complete yet, I think
it would be better to add one since we've done many works for C++20
Modules in clang15.

Differential Revision: https://reviews.llvm.org/D129138

clang/docs/ReleaseNotes.rst

@@ -513,6 +513,14 @@ C++20 Feature Support
   that can be used for such compatibility. The demangler now demangles
   symbols with named module attachment.
 
+- Enhanced the support for C++20 Modules, including: Partitions,
+  Reachability, Header Unit and ``extern "C++"`` semantics.
+
+- Implemented `P1103R3: Merging Modules <https://wg21.link/P1103R3>`_.
+- Implemented `P1779R3: ABI isolation for member functions <https://wg21.link/P1779R3>`_.
+- Implemented `P1874R1: Dynamic Initialization Order of Non-Local Variables in Modules <https://wg21.link/P1874R1>`_.
+- Partially implemented `P1815R2: Translation-unit-local entities <https://wg21.link/P1815R2>`_.
+
 - As per "Conditionally Trivial Special Member Functions" (P0848), it is
   now possible to overload destructors using concepts. Note that the rest
   of the paper about other special member functions is not yet implemented.

clang/www/cxx_status.html

@@ -1164,7 +1164,7 @@ code. This issue is expected to be rectified soon.
     <tr>
       <td rowspan="10">Modules</td>
       <td><a href="https://wg21.link/p1103r3">P1103R3</a></td>
-      <td class="partial" align="center">Partial</td>
+      <td class="unreleased" align="center">Clang 15</td>
     </tr>
       <tr> <!-- from Cologne -->
         <td><a href="https://wg21.link/p1766r1">P1766R1</a> (<a href="#dr">DR</a>)</td>
@@ -1180,17 +1180,19 @@ code. This issue is expected to be rectified soon.
       </tr>
       <tr> <!-- from Belfast -->
         <td><a href="https://wg21.link/p1874r1">P1874R1</a></td>
-        <td class="partial" align="center">Partial</td>
+        <td class="unreleased" align="center">Clang 15</td>
       </tr>
       <tr> <!-- from Belfast -->
         <td><a href="https://wg21.link/p1979r0">P1979R0</a></td>
-        <td rowspan="3" class="none" align="center">No</td>
+        <td class="none" align="center">No</td>
       </tr>
       <tr> <!-- from Prague -->
         <td><a href="https://wg21.link/p1779r3">P1779R3</a></td>
+        <td class="unreleased" align="center">Clang 15</td>
       </tr>
       <tr>
         <td><a href="https://wg21.link/p1857r3">P1857R3</a></td>
+        <td class="none" align="center">No</td>
       </tr>
       <tr>
         <td><a href="https://wg21.link/p2115r0">P2115R0</a></td>
@@ -1198,7 +1200,7 @@ code. This issue is expected to be rectified soon.
       </tr>
       <tr>
         <td><a href="https://wg21.link/p1815r2">P1815R2</a></td>
-        <td class="none" align="center">No</td>
+        <td class="partial" align="center">Partial</td>
       </tr>
     <tr>
       <td>Coroutines</td>