[clang] [Fuchsia] Set LIBCXX_ABI_UNSTABLE instead of LIBCXX_ABI_VERSION (PR #189123)

[Roland McGrath via cfe-commits]

https://github.com/frobtech updated https://github.com/llvm/llvm-project/pull/189123

>From 3474b56c79ccf4ac9cfaa5bb3297df192161d6a7 Mon Sep 17 00:00:00 2001
From: Roland McGrath <mcgrathr at google.com>
Date: Fri, 27 Mar 2026 15:27:19 -0700
Subject: [PATCH 1/2] [Fuchsia] Set LIBCXX_ABI_UNSTABLE instead of
 LIBCXX_ABI_VERSION

Use the generic switch rather than encoding the version number it
currently corresponds to.
---
 clang/cmake/caches/Fuchsia-stage2.cmake | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/clang/cmake/caches/Fuchsia-stage2.cmake b/clang/cmake/caches/Fuchsia-stage2.cmake
index 4944d1ffdf588..ccd127094382a 100644
--- a/clang/cmake/caches/Fuchsia-stage2.cmake
+++ b/clang/cmake/caches/Fuchsia-stage2.cmake
@@ -127,7 +127,7 @@ if(WIN32 OR LLVM_WINSYSROOT)
   list(APPEND RUNTIME_TARGETS "${target}")
   set(RUNTIMES_${target}_CMAKE_SYSTEM_NAME Windows CACHE STRING "")
   set(RUNTIMES_${target}_CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "")
-  set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
+  set(RUNTIMES_${target}_LIBCXX_ABI_UNSTABLE ON CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_ABI_LINKER_SCRIPT OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx" CACHE STRING "")
@@ -180,7 +180,7 @@ foreach(target aarch64-unknown-linux-gnu;armv7-unknown-linux-gnueabihf;i386-unkn
     set(RUNTIMES_${target}_LIBCXX_USE_COMPILER_RT ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
-    set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
+    set(RUNTIMES_${target}_LIBCXX_ABI_UNSTABLE ON CACHE STRING "")
     set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}_SANITIZER_CXX_ABI "libc++" CACHE STRING "")
     set(RUNTIMES_${target}_SANITIZER_CXX_ABI_INTREE ON CACHE BOOL "")
@@ -250,7 +250,7 @@ if(FUCHSIA_SDK)
     set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
     set(RUNTIMES_${target}_LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY OFF CACHE BOOL "")
-    set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
+    set(RUNTIMES_${target}_LIBCXX_ABI_UNSTABLE ON CACHE STRING "")
     set(RUNTIMES_${target}_LLVM_ENABLE_ASSERTIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")
 
@@ -358,7 +358,7 @@ foreach(target armv6m-none-eabi;armv7m-none-eabi;armv7em-none-eabi;armv8m.main-n
   endforeach()
   set(RUNTIMES_${target}_LLVM_LIBC_FULL_BUILD ON CACHE BOOL "")
   set(RUNTIMES_${target}_LIBC_ENABLE_USE_BY_CLANG ON CACHE BOOL "")
-  set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
+  set(RUNTIMES_${target}_LIBCXX_ABI_UNSTABLE ON CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_CXX_ABI none CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC ON CACHE BOOL "")
@@ -416,7 +416,7 @@ foreach(target riscv32-unknown-elf)
   endforeach()
   set(RUNTIMES_${target}_LLVM_LIBC_FULL_BUILD ON CACHE BOOL "")
   set(RUNTIMES_${target}_LIBC_ENABLE_USE_BY_CLANG ON CACHE BOOL "")
-  set(RUNTIMES_${target}_LIBCXX_ABI_VERSION 2 CACHE STRING "")
+  set(RUNTIMES_${target}_LIBCXX_ABI_UNSTABLE ON CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_CXX_ABI none CACHE STRING "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
   set(RUNTIMES_${target}_LIBCXX_ENABLE_STATIC ON CACHE BOOL "")

>From dcaf5895e58de56eebfc8e1955444fce3fb60fb3 Mon Sep 17 00:00:00 2001
From: Roland McGrath <mcgrathr at google.com>
Date: Fri, 27 Mar 2026 15:55:53 -0700
Subject: [PATCH 2/2] Same for APPLE

---
 clang/cmake/caches/Fuchsia-stage2.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/cmake/caches/Fuchsia-stage2.cmake b/clang/cmake/caches/Fuchsia-stage2.cmake
index ccd127094382a..7f95fbf54d4c3 100644
--- a/clang/cmake/caches/Fuchsia-stage2.cmake
+++ b/clang/cmake/caches/Fuchsia-stage2.cmake
@@ -78,7 +78,7 @@ if(APPLE)
   set(LIBCXXABI_INSTALL_LIBRARY OFF CACHE BOOL "")
   set(LIBCXXABI_USE_COMPILER_RT ON CACHE BOOL "")
   set(LIBCXXABI_USE_LLVM_UNWINDER ON CACHE BOOL "")
-  set(LIBCXX_ABI_VERSION 2 CACHE STRING "")
+  set(LIBCXX_ABI_UNSTABLE ON CACHE STRING "")
   set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
   set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
   set(LIBCXX_HARDENING_MODE "none" CACHE STRING "")