CMAKE ignores all settings about specifying the compiler - c++

Question

On Windows 10 with VS2017 and LLVM installed
and CMAKE just takes VC compiler as default and ignores both set command in the CMakeLists.txt and command line -DCMAKE_CXX_COMPILER
I have no idea how to make it use LLVM Clang
I checked out many existing questions but they do not work for me
CMakeLists.txt
cmake_minimum_required(VERSION 3.11)
set(CMAKE_CXX_COMPILER "C:\\Program Files\\LLVM\\bin\\Clang++")
project(CMakeTest1 VERSION 0.0.0 LANGUAGES CXX)
aux_source_directory(. MAINDIR)
add_executable(CMakeTest1 ${MAINDIR})
main.cpp
#include <iostream>
using namespace std;
int main()
{
cout << "Hello World!" << endl;
return 0;
}
running command with git bash
***#DESKTOP-8KJ4J0H MINGW64 /d/CMakeTest1
$ cmake -DCMAKE_CXX_COMPILER="C:\Program Files\LLVM\bin\Clang++" .
-- Building for: Visual Studio 15 2017
-- The CXX compiler identification is MSVC 19.13.26129.0
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.13.26128/bin/Hostx86/x86/cl.exe
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.13.26128/bin/Hostx86/x86/cl.exe -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: D:/CMakeTest1
my CXX compiler identification is forced to be MSVC and cannot be changed by any method.
no idea why
EDITED:
what i wanna strongly declare is, i swear and clearly know that i CLEANED ALL GENERATED FILES form the folder and there are ONLY JUST CMakeLists.txt and main.cpp existing. and I DON'T WANT TO BE ASSUMED having old cache files unremoved

Answer 1

This may be due to default generator of CMake in Windows.
-- Building for: Visual Studio 15 2017
...
You can change the generator by adding -G <generator name> to the command line. In your case, I think -G 'MSYS Makefiles' may work.

Answer 2

This happens because CMAKE_CXX_COMPILER was inferred from your generator (The latest Visual Studio is used by default on windows), so it is cl.exe.
In order to switch to clang you should use other generator e.g. Ninja or Unix Makefiles.
If you want to use VS with clang-cl.exe, you need to set platform toolset to appropriate version by adding flag -TLLVM-vs2014.
See this instructions for more info.