[llvm] deprecate LLVM_ENABLE_PROJECTS in favor of LLVM_ENABLE_RUNTIMES (PR #117265)

[Nick Desaulniers via llvm-commits]

https://github.com/nickdesaulniers created https://github.com/llvm/llvm-project/pull/117265

We plan to make this a hard error in the LLVM 21 release.

Link: #78479


>From 1194df97a9b15d3de1e01f3caeaf2b38b6380a01 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Thu, 21 Nov 2024 15:54:26 -0800
Subject: [PATCH] deprecate LLVM_ENABLE_PROJECTS in favor of
 LLVM_ENABLE_RUNTIMES

We plan to make this a hard error in the LLVM 21 release.

Link: #78479
---
 llvm/CMakeLists.txt | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index cfcf1404d82b7c..569c01b61daac0 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -150,6 +150,13 @@ if ("flang" IN_LIST LLVM_ENABLE_PROJECTS)
   endif()
 endif()
 
+if ("libc" IN_LIST LLVM_ENABLE_PROJECTS)
+  message(WARNING "Using LLVM_ENABLE_PROJECTS=libc is deprecated now, and will "
+    "become a fatal error in the LLVM 21 release.  Please use "
+    "-DLLVM_ENABLE_RUNTIMES=libc or see the instructions at "
+    "https://libc.llvm.org/ for building the runtimes.")
+endif()
+
 # Select the runtimes to build
 #
 # As we migrate runtimes to using the bootstrapping build, the set of default runtimes