[compiler-rt] [compiler-rt][www] replace deprecated LLVM_CONFIG_PATH with LLVM_CMAKE_DIR (PR #71500)

[Vitaly Buka via llvm-commits]

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@@ -123,7 +123,7 @@ <h2>Get it and get involved!</h2>
   <li>cd llvm-project</li>
   <li>mkdir build-compiler-rt</li>
   <li>cd build-compiler-rt</li>
-  <li>cmake ../compiler-rt -DLLVM_CONFIG_PATH=/path/to/llvm-config</li>
+  <li>cmake ../compiler-rt -DLLVM_CMAKE_DIR=/path/to/llvm-project/cmake/modules</li>
----------------
vitalybuka wrote:

No, it still does not work - `ninja` just copy a few headers and that's it

`-DLLVM_CMAKE_DIR=/full_path_to_llvm_build_dir/` works as expected, but I am not sure if that was expected.

```
cd llvm-project/
cmake -GNinja -B ../out/compiler-rt -S ./compiler-rt -DLLVM_CMAKE_DIR=$(readlink -f ../out/llvm_build) -DCMAKE_C_COMPILER=$(readlink -f ../out/llvm_build/bin/clang) -DCMAKE_CXX_COMPILER=$(readlink -f ../out/llvm_build/bin/clang++)
ninja -C ../out/compiler-rt
ninja -C ../out/compiler-rt check-all
```


https://github.com/llvm/llvm-project/pull/71500