[runtimes] Remove support for standalone builds

Standalone build have been deprecated for some time now, so this
commit removes support for those builds entirely from libc++, libc++abi
and libunwind.

This, along with the removal of other legacy ways to build, will allow
for major build system simplifications.

Differential Revision: https://reviews.llvm.org/D119255

GitOrigin-RevId: 6f17768e11480063f4c2bcbeea559505fee3ea19
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ecbc709..f40ee88 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -28,6 +28,10 @@
         "Specify path to libc++ source.")
+  message(FATAL_ERROR "The Standalone build has been deprecated since LLVM 14, and it is not supported anymore. "
+                      "Please use one of the ways described at https://libcxx.llvm.org/BuildingLibcxx.html for "
+                      "building libc++abi.")
   project(libcxxabi CXX C)
   set(PACKAGE_NAME libcxxabi)
diff --git a/www/index.html b/www/index.html
index b6275e6..8803504 100644
--- a/www/index.html
+++ b/www/index.html
@@ -73,51 +73,13 @@
   <h2>Get it and get involved!</h2>
-  <p>To check out the code (including llvm and others), use:</p>
-  <ul>
-  <li><code>git clone https://github.com/llvm/llvm-project.git</code></li>
-  </ul>
-  <p>To build:</p>
-  <ul>
-  <li><code>cd llvm-project</code></li>
-  <li><code>mkdir build &amp;&amp; cd build</code></li>
-  <li><code>cmake -DLLVM_ENABLE_PROJECTS=libcxxabi ../llvm # on linux you may need to specify -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
-  <li><code>make</code></li>
-  </ul>
-  <p>To do a standalone build:</p>
-  <ul>
-  <li>
-    Check out the source tree. This includes the other subprojects, but you'll only use the libcxxabi part.
-  </li>
-  <li><code>cd llvm-project</code></li>
-  <li><code>mkdir build-libcxxabi &amp;&amp; cd build-libcxxabi</code></li>
-  <li><code>cmake ../libcxxabi # on linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
-  <li><code>make</code></li>
-  </ul>
-  <p> By default CMake uses <code>llvm-config</code> to locate the required
-      LLVM sources. If CMake cannot find <code>llvm-config</code> then you must
-      configure CMake using either of the following options.
-  </p>
-  <ul>
-  <li><code>-DLLVM_CONFIG_PATH=path/to/llvm-config</code></li>
-  <li><code>-DLLVM_PATH=path/to/llvm-source-root</code></li>
-  </ul>
+  <p>For building libc++abi, please see the libc++ documentation on
+     <a href="https://libcxx.llvm.org/BuildingLibcxx.html">building the runtimes</a>.
-  <p>To run the tests:</p>
-  <ul>
-  <li><code>make check-cxxabi</code></li>
-  </ul>
-  <p>Note: in a standalone build, the system's libc++ will be used for tests. If
-  the system's libc++ was statically linked against libc++abi (or linked against
-  a different ABI library), this may interfere with test results.</p>
-  <p>Send discussions to the
-  (<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev mailing list</a>).</p>
+  <p>For getting involved with libc++abi, please see the libc++ documentation on
+      <a href="https://libcxx.llvm.org/Contributing.html">getting involved</a>.
+  </p>
   <h2>Frequently asked questions</h2>