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

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``````````diff
--- compute_projects.py	2025-10-09 21:00:22.000000 +0000
+++ compute_projects.py	2025-10-09 21:05:35.019176 +0000
@@ -104,13 +104,13 @@
     "bolt",  # No Windows Support.
     "libcxx",
     "libcxxabi",
     "libunwind",
     "flang-rt",
-    "mlir",  #CAROLINE
-    "polly", #CAROLINE
-    "lld",   #CAROLINE
+    "mlir",  # CAROLINE
+    "polly",  # CAROLINE
+    "lld",  # CAROLINE
 }
 
 # These are projects that we should test if the project itself is changed but
 # where testing is not yet stable enough for it to be enabled on changes to
 # dependencies.

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