[llvm] [cmake] Serialize native builds for Make generator (PR #121021)

[via llvm-commits]

https://github.com/arthurqiu updated https://github.com/llvm/llvm-project/pull/121021

>From d3c3711e2ac030a2edc9c8a49b4c6c213615763a Mon Sep 17 00:00:00 2001
From: Arthurq Qiu <arthurq at nvidia.com>
Date: Mon, 23 Dec 2024 18:09:31 -0800
Subject: [PATCH] FileLock.cmake to serialize sub-make build for native targets

---
 llvm/cmake/modules/FileLock.cmake                 | 9 +++++++++
 llvm/cmake/modules/LLVMExternalProjectUtils.cmake | 6 +++++-
 2 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 llvm/cmake/modules/FileLock.cmake

diff --git a/llvm/cmake/modules/FileLock.cmake b/llvm/cmake/modules/FileLock.cmake
new file mode 100644
index 00000000000000..0ee40a68333f2a
--- /dev/null
+++ b/llvm/cmake/modules/FileLock.cmake
@@ -0,0 +1,9 @@
+# CMake script that synchronizes process execution on a given file lock.
+#
+# Input variables:
+#   LOCK_FILE_PATH    - The file to be locked for the scope of the process of this cmake script.
+#   COMMAND           - The command to be executed.
+
+file(LOCK ${LOCK_FILE_PATH})
+separate_arguments(command_args NATIVE_COMMAND "${COMMAND}")
+execute_process(COMMAND ${command_args} COMMAND_ERROR_IS_FATAL ANY)
diff --git a/llvm/cmake/modules/LLVMExternalProjectUtils.cmake b/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
index f7e1165bc4b947..3e843f178f6af5 100644
--- a/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
+++ b/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
@@ -9,7 +9,11 @@ function(llvm_ExternalProject_BuildCmd out_var target bin_dir)
   endif()
   if (CMAKE_GENERATOR MATCHES "Make")
     # Use special command for Makefiles to support parallelism.
-    set(${out_var} "$(MAKE)" "-C" "${bin_dir}" "${target}" PARENT_SCOPE)
+    set(make_cmd "$(MAKE)" "-C" "${bin_dir}" "${target}")
+    set(file_lock_script "${LLVM_CMAKE_DIR}/FileLock.cmake")
+    set(${out_var} ${CMAKE_COMMAND} "-DLOCK_FILE_PATH=${bin_dir}/cmake.lock"
+                                    "-DCOMMAND='${make_cmd}'"
+                                    -P "${file_lock_script}" PARENT_SCOPE)
   else()
     set(tool_args "${LLVM_EXTERNAL_PROJECT_BUILD_TOOL_ARGS}")
     if(NOT tool_args STREQUAL "")