[llvm] [cmake] Set up llvm-ml as ASM_MASM tool in WinMsvc.cmake (PR #104903)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo created https://github.com/llvm/llvm-project/pull/104903

Nowadays, an ASM_MASM tool is required for building the BLAKE3 assembly in llvm/lib/Support - the llvm-ml tool can do this.

>From 181dbd377b7aee2eca4c7d87bfe0f6d22411948f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin at martin.st>
Date: Tue, 20 Aug 2024 11:17:32 +0300
Subject: [PATCH] [cmake] Set up llvm-ml as ASM_MASM tool in WinMsvc.cmake

Nowadays, an ASM_MASM tool is required for building the BLAKE3
assembly in llvm/lib/Support - the llvm-ml tool can do this.
---
 llvm/cmake/platforms/WinMsvc.cmake | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/llvm/cmake/platforms/WinMsvc.cmake b/llvm/cmake/platforms/WinMsvc.cmake
index 77c3ab3d8fc11d..e5d1ba8ec4a7c2 100644
--- a/llvm/cmake/platforms/WinMsvc.cmake
+++ b/llvm/cmake/platforms/WinMsvc.cmake
@@ -240,6 +240,7 @@ set(CMAKE_C_COMPILER "${LLVM_NATIVE_TOOLCHAIN}/bin/clang-cl" CACHE FILEPATH "")
 set(CMAKE_CXX_COMPILER "${LLVM_NATIVE_TOOLCHAIN}/bin/clang-cl" CACHE FILEPATH "")
 set(CMAKE_LINKER "${LLVM_NATIVE_TOOLCHAIN}/bin/lld-link" CACHE FILEPATH "")
 set(CMAKE_AR "${LLVM_NATIVE_TOOLCHAIN}/bin/llvm-lib" CACHE FILEPATH "")
+set(CMAKE_ASM_MASM_COMPILER "${LLVM_NATIVE_TOOLCHAIN}/bin/llvm-ml" CACHE FILEPATH "")
 
 # Even though we're cross-compiling, we need some native tools (e.g. llvm-tblgen), and those
 # native tools have to be built before we can start doing the cross-build.  LLVM supports
@@ -275,6 +276,9 @@ endif()
 string(REPLACE ";" " " COMPILE_FLAGS "${COMPILE_FLAGS}")
 string(APPEND CMAKE_C_FLAGS_INIT " ${COMPILE_FLAGS}")
 string(APPEND CMAKE_CXX_FLAGS_INIT " ${COMPILE_FLAGS}")
+if(TRIPLE_ARCH STREQUAL "x86_64")
+  string(APPEND CMAKE_ASM_MASM_FLAGS_INIT " -m64")
+endif()
 
 set(LINK_FLAGS
     # Prevent CMake from attempting to invoke mt.exe. It only recognizes the slashed form and not the dashed form.