[llvm] [libc][cmake] Make libc not included in LLVM_ENABLE_PROJECTS=all. (PR #142626)

[via llvm-commits]

https://github.com/lntue updated https://github.com/llvm/llvm-project/pull/142626

>From e405536a584987a50beb3cae1bbfa1258766b6fd Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue.h at gmail.com>
Date: Tue, 3 Jun 2025 14:56:49 +0000
Subject: [PATCH 1/2] [libc][cmake] Make libc not included in
 LLVM_ENABLE_PROJECTS=all.

---
 llvm/CMakeLists.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index ed44b16bf9aeb..5b08b2839d828 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -108,7 +108,7 @@ endif()
 # LLVM_EXTERNAL_${project}_SOURCE_DIR using LLVM_ALL_PROJECTS
 # This allows an easy way of setting up a build directory for llvm and another
 # one for llvm+clang+... using the same sources.
-set(LLVM_ALL_PROJECTS "bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libc;libclc;lld;lldb;mlir;openmp;polly;pstl")
+set(LLVM_ALL_PROJECTS "bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libclc;lld;lldb;mlir;openmp;polly;pstl")
 if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
   # Disallow 'openmp' as a LLVM PROJECT on AIX as the supported way is to use
   # LLVM_ENABLE_RUNTIMES.
@@ -116,7 +116,7 @@ if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
 endif()
 
 # The flang project is not yet part of "all" projects (see C++ requirements)
-set(LLVM_EXTRA_PROJECTS "flang")
+set(LLVM_EXTRA_PROJECTS "flang" "libc")
 # List of all known projects in the mono repo
 set(LLVM_KNOWN_PROJECTS "${LLVM_ALL_PROJECTS};${LLVM_EXTRA_PROJECTS}")
 set(LLVM_ENABLE_PROJECTS "" CACHE STRING

>From eb3a0c9512a963ddc01b202cf2fd86c816e93652 Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue.h at gmail.com>
Date: Wed, 4 Jun 2025 18:27:15 +0000
Subject: [PATCH 2/2] Update comments.

---
 llvm/CMakeLists.txt | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index 5b08b2839d828..3ae7fac5bc3cf 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -115,7 +115,11 @@ if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
   list(REMOVE_ITEM LLVM_ALL_PROJECTS openmp)
 endif()
 
-# The flang project is not yet part of "all" projects (see C++ requirements)
+# The "libc" project, which is not part of "all" projects, could be included in
+# LLVM_ENABLE_PROJECTS.  It is preferred to include "libc" in
+# LLVM_ENABLE_RUNTIMES instead of LLVM_ENABLE_PROJECTS.
+#
+# The flang project is not yet part of "all" projects (see C++ requirements).
 set(LLVM_EXTRA_PROJECTS "flang" "libc")
 # List of all known projects in the mono repo
 set(LLVM_KNOWN_PROJECTS "${LLVM_ALL_PROJECTS};${LLVM_EXTRA_PROJECTS}")
@@ -167,8 +171,7 @@ if ("flang" IN_LIST LLVM_ENABLE_PROJECTS)
 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 "
+  message(WARNING "Using LLVM_ENABLE_PROJECTS=libc is deprecated.  Please use "
     "-DLLVM_ENABLE_RUNTIMES=libc or see the instructions at "
     "https://libc.llvm.org/ for building the runtimes.")
 endif()