[Bug] CMake minimum version too low

[varunsh-xilinx]

The CMake version in CMakeLists.txt here is too low at 3.18. New changes require at least 3.20.0:

• In ubuntu_install_cmake_source.sh, the default version is set to 3.20.0 with a note that LLVM 16+ requires it.
• [Fix] Broken Windows Build with LLVM #16081 adds cmake_path to cmake/utils/FindLLVM.cmake. This command exists in CMake 3.20+.

Expected behavior

If the CMake version is unsupported, it should fail at cmake_minimum_required().

Actual behavior

The build failed in FindLLVM.cmake when cmake_path couldn't be found as a CMake command:

CMake Error at cmake/utils/FindLLVM.cmake:121 (cmake_path):
  Unknown CMake command "cmake_path".
Call Stack (most recent call first):
  cmake/modules/LLVM.cmake:31 (find_llvm)
  CMakeLists.txt:528 (include)

Environment

Tried on a custom Ubuntu 20.04 container with TVM commit a9fcac1.

Steps to reproduce

Attempt to build TVM with CMake 3.19.1.

Triage

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• needs-triage