[llvm] [runtimes] Propagate CMAKE_OSX_ARCHITECTURES on Darwin (PR #196877)

[via llvm-commits]

https://github.com/hrtan99 updated https://github.com/llvm/llvm-project/pull/196877

>From 96d87471b30da17f353321227bcadad8597b5f54 Mon Sep 17 00:00:00 2001
From: hrtan <htanaj at cse.ust.hk>
Date: Mon, 11 May 2026 13:02:25 +0800
Subject: [PATCH] [runtimes] Propagate CMAKE_OSX_ARCHITECTURES on Darwin

---
 llvm/runtimes/CMakeLists.txt | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
index 812cd387c6596..b9bdbad1ede12 100644
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -4,9 +4,15 @@
 # the two files.
 
 set(COMMON_CMAKE_ARGS "-DHAVE_LLVM_LIT=ON;-DCLANG_RESOURCE_DIR=${CLANG_RESOURCE_DIR}")
-if(APPLE AND CMAKE_OSX_SYSROOT AND (LLVM_TARGET_TRIPLE STREQUAL LLVM_HOST_TRIPLE))
-  # Only propagate the host sysroot for native runtimes builds.
-  list(APPEND RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_SYSROOT=${CMAKE_OSX_SYSROOT}")
+if(APPLE AND (LLVM_TARGET_TRIPLE STREQUAL LLVM_HOST_TRIPLE))
+  # Keep native Apple runtimes builds aligned with the top-level SDK/arch
+  # selection instead of letting subprojects rediscover broader defaults.
+  if(CMAKE_OSX_SYSROOT)
+    list(APPEND RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_SYSROOT=${CMAKE_OSX_SYSROOT}")
+  endif()
+  if(CMAKE_OSX_ARCHITECTURES)
+    list(APPEND RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_ARCHITECTURES=${CMAKE_OSX_ARCHITECTURES}")
+  endif()
 endif()
 foreach(proj ${LLVM_ENABLE_RUNTIMES})
   string(TOUPPER "${proj}" canon_name)