[llvm] [cmake] Forward MacOS sysroot to runtimes when not crosscompiling (PR #182501)

[Tom Eccles via llvm-commits]

https://github.com/tblah updated https://github.com/llvm/llvm-project/pull/182501

>From 4253b70470ea9f765c255e72e00bc8dc2e0b6955 Mon Sep 17 00:00:00 2001
From: Tom Eccles <tom.eccles at arm.com>
Date: Thu, 19 Feb 2026 13:58:25 +0000
Subject: [PATCH 1/3] [cmake] Forward MacOS sysroot to runtimes when not
 crosscompiling

The LLVM build documentation says that setting CMAKE_OSX_SYSROOT should
be sufficient to correctly configure the sysroot, however this flag was
not forwarded to the build of runtimes: leading to failures in flang-rt
tests. https://llvm.org/docs/CMake.html#apple-osx

It is not safe to forward this flag in general because the runtime might
be cross-compiled. In this case I have tried to do this only for native
builds. My intention here is not to make the build more complex than
currently documented.
---
 llvm/runtimes/CMakeLists.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
index 7d0ee620dcffa..94eb9df28a8e9 100644
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -4,6 +4,11 @@
 # the two files.
 
 set(COMMON_CMAKE_ARGS "-DHAVE_LLVM_LIT=ON;-DCLANG_RESOURCE_DIR=${CLANG_RESOURCE_DIR}")
+set(NATIVE_RUNTIMES_CMAKE_ARGS)
+if(APPLE AND CMAKE_OSX_SYSROOT AND (LLVM_TARGET_TRIPLE STREQUAL LLVM_HOST_TRIPLE))
+  # Only propagate the host sysroot for native runtimes builds.
+  list(APPEND NATIVE_RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_SYSROOT=${CMAKE_OSX_SYSROOT}")
+endif()
 foreach(proj ${LLVM_ENABLE_RUNTIMES})
   string(TOUPPER "${proj}" canon_name)
   STRING(REGEX REPLACE "-" "_" canon_name ${canon_name})
@@ -298,6 +303,7 @@ function(runtime_default_target)
                                       -DCMAKE_Fortran_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       ${COMMON_CMAKE_ARGS}
+                                      ${NATIVE_RUNTIMES_CMAKE_ARGS}
                                       ${RUNTIMES_CMAKE_ARGS}
                                       ${ARG_CMAKE_ARGS}
                            PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES

>From eecf1093c29471b858252d955db72c533a9ac2e9 Mon Sep 17 00:00:00 2001
From: Tom Eccles <tom.eccles at arm.com>
Date: Fri, 20 Feb 2026 16:33:26 +0000
Subject: [PATCH 2/3] Fix variable setting

---
 llvm/runtimes/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
index 94eb9df28a8e9..bac1f0a03728b 100644
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -4,7 +4,7 @@
 # the two files.
 
 set(COMMON_CMAKE_ARGS "-DHAVE_LLVM_LIT=ON;-DCLANG_RESOURCE_DIR=${CLANG_RESOURCE_DIR}")
-set(NATIVE_RUNTIMES_CMAKE_ARGS)
+set(NATIVE_RUNTIMES_CMAKE_ARGS "")
 if(APPLE AND CMAKE_OSX_SYSROOT AND (LLVM_TARGET_TRIPLE STREQUAL LLVM_HOST_TRIPLE))
   # Only propagate the host sysroot for native runtimes builds.
   list(APPEND NATIVE_RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_SYSROOT=${CMAKE_OSX_SYSROOT}")

>From f2cb7524f3439e8373ef9d6feffd01e20b975749 Mon Sep 17 00:00:00 2001
From: Tom Eccles <tom.eccles at arm.com>
Date: Thu, 23 Apr 2026 15:56:03 +0100
Subject: [PATCH 3/3] Use RUNTIMES_CMAKE_ARGS

---
 llvm/runtimes/CMakeLists.txt | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
index bac1f0a03728b..74c4940a1534c 100644
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -4,10 +4,9 @@
 # the two files.
 
 set(COMMON_CMAKE_ARGS "-DHAVE_LLVM_LIT=ON;-DCLANG_RESOURCE_DIR=${CLANG_RESOURCE_DIR}")
-set(NATIVE_RUNTIMES_CMAKE_ARGS "")
 if(APPLE AND CMAKE_OSX_SYSROOT AND (LLVM_TARGET_TRIPLE STREQUAL LLVM_HOST_TRIPLE))
   # Only propagate the host sysroot for native runtimes builds.
-  list(APPEND NATIVE_RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_SYSROOT=${CMAKE_OSX_SYSROOT}")
+  list(APPEND RUNTIMES_CMAKE_ARGS "-DCMAKE_OSX_SYSROOT=${CMAKE_OSX_SYSROOT}")
 endif()
 foreach(proj ${LLVM_ENABLE_RUNTIMES})
   string(TOUPPER "${proj}" canon_name)
@@ -303,7 +302,6 @@ function(runtime_default_target)
                                       -DCMAKE_Fortran_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       ${COMMON_CMAKE_ARGS}
-                                      ${NATIVE_RUNTIMES_CMAKE_ARGS}
                                       ${RUNTIMES_CMAKE_ARGS}
                                       ${ARG_CMAKE_ARGS}
                            PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES