[compiler-rt] [compiler-rt] Fix CMake configure on Windows (PR #90843)

[David Spickett via llvm-commits]

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@@ -369,7 +369,11 @@ macro(construct_compiler_rt_default_triple)
   endif()
 
   if ("${CMAKE_C_COMPILER_ID}" MATCHES "Clang")
-    execute_process(COMMAND ${CMAKE_C_COMPILER} --target=${COMPILER_RT_DEFAULT_TARGET_TRIPLE} -print-target-triple
+    set(cmd_prefix "")
+    if (CMAKE_C_SIMULATE_ID MATCHES "MSVC")
+      set(cmd_prefix "/clang:")
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DavidSpickett wrote:

This does what exactly?

I guess that it marks the following option as a normal clang style option `/clang: -something-like-this` instead of a `/option` which cl.exe would be expecting.

https://github.com/llvm/llvm-project/pull/90843