[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
NOKEYCHECK=True
GitOrigin-RevId: 6f17768e11480063f4c2bcbeea559505fee3ea19
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 9bb06cf..0bf24b9 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -57,3 +57,7 @@
Build System Changes
--------------------
+
+- Support for standalone builds have been entirely removed from libc++, libc++abi and
+ libunwind. Please use :ref:`these instructions <build instructions>` for building
+ libc++, libc++abi and/or libunwind.