Boot2Qt toolchains don't work with CMake

-- The CXX compiler identification is unknown
CMake Error at CMakeLists.txt:3 (project):
  The CMAKE_CXX_COMPILER:

    /home/user/Qt/5.15.10/Boot2Qt/intel-corei7-64/toolchain/sysroots/x86_64-pokysdk-linux/usr/bin/corei7-64-poky-linux/corei7-64-poky-linux-g++

  is not a full path to an existing compiler tool.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.