[clang] [compiler-rt] [llvm] [CMake] Use Clang to infer the target triple (PR #89425)

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BukeBeyond wrote:

The interesting part is the first time LLVM was built, there were no problems, because the compiler was switched to clang++ and Cmake probably updated CMAKE_C_SIMULATE_ID correctly.  But the subsequent incremental builds using caches, the CMAKE_C_SIMULATE_ID started inhering MSVC from the main build despite switching to Clang++.  This may be a bug in CMake perhaps.

https://github.com/llvm/llvm-project/pull/89425