[clang] [clang][CMake][Darwin] Make HOST_LINK_VERSION a CACHE option on Darwin (PR #203917)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: yueshe

<details>
<summary>Changes</summary>

This allows specifying a fixed host linker version during Clang configuration (e.g. -DHOST_LINK_VERSION=1249), bypassing the default auto-detection. This is useful for hermetic packaging scripts where the auto-detected host linker might differ from the intended target linker, and we do not want certain features to be enabled that depends on the host linker version -- e.g. https://github.com/llvm/llvm-project/issues/203385


---
Full diff: https://github.com/llvm/llvm-project/pull/203917.diff


1 Files Affected:

- (modified) clang/CMakeLists.txt (+5-2) 


``````````diff
diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index db79131af9c1f..cd7ba53b03061 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -407,9 +407,12 @@ if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
 endif ()
 
 # Determine HOST_LINK_VERSION on Darwin.
-set(HOST_LINK_VERSION)
-if (APPLE AND NOT CMAKE_LINKER MATCHES ".*lld.*")
+set(HOST_LINK_VERSION "" CACHE STRING "Host linker version on Darwin")
+if (APPLE AND NOT HOST_LINK_VERSION AND NOT CMAKE_LINKER MATCHES ".*lld.*")
   get_darwin_linker_version(HOST_LINK_VERSION)
+  set(HOST_LINK_VERSION "${HOST_LINK_VERSION}" CACHE STRING "Host linker version on Darwin" FORCE)
+endif()
+if (HOST_LINK_VERSION)
   message(STATUS "Host linker version: ${HOST_LINK_VERSION}")
 endif()
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/203917