[llvm] [CI] Update Windows testing to use clang compiler. (PR #162026)

[via llvm-commits]

https://github.com/cmtice updated https://github.com/llvm/llvm-project/pull/162026

>From e5106e4ed70a772096aa5c73a7072ef50b966a74 Mon Sep 17 00:00:00 2001
From: Caroline Tice <cmtice at google.com>
Date: Sun, 5 Oct 2025 12:39:44 -0700
Subject: [PATCH 1/2] [CI] Update Windows testing to use clang compiler.

Test whether or not using clang for premerge testing on Windows
will improve performance.

Currently a work-in-progress: DO NOT REVIEW! DO NOT COMMIT!
---
 .ci/monolithic-windows.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index f85d6e3d51b57..5ad4899188f20 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -23,8 +23,8 @@ runtimes_targets="${4}"
 start-group "CMake"
 pip install -q -r "${MONOREPO_ROOT}"/.ci/all_requirements.txt
 
-export CC=cl
-export CXX=cl
+export CC=clang-cl
+export CXX=clang-cl
 export LD=link
 
 # The CMAKE_*_LINKER_FLAGS to disable the manifest come from research

>From cc89d8c05a39685f84b0e4e24d962a00611c4feb Mon Sep 17 00:00:00 2001
From: Caroline Tice <cmtice at google.com>
Date: Sun, 5 Oct 2025 12:50:04 -0700
Subject: [PATCH 2/2] Try to find clang compiler.

---
 .ci/monolithic-windows.sh | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index 5ad4899188f20..51cde5f4fc878 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -23,6 +23,8 @@ runtimes_targets="${4}"
 start-group "CMake"
 pip install -q -r "${MONOREPO_ROOT}"/.ci/all_requirements.txt
 
+which clang-cl
+
 export CC=clang-cl
 export CXX=clang-cl
 export LD=link