Issue with OPENMP_RUNTIME set to "COMP"

If I set `OPENMP_RUNTIME` to `COMP`, cmake will add `/openmp` flag to msvc, but later on it will be test

`OpenMP_CXX_FOUND` variable causing the build to failed with error `OpenMP not found`.



CMakeLists.txt reference:

```cmake

if(NOT OPENMP_RUNTIME STREQUAL "NONE")

  if(WIN32)

    add_compile_options("/openmp")

  else()

    find_package(OpenMP)

    if(OpenMP_CXX_FOUND)

      add_compile_options(${OpenMP_CXX_FLAGS})

    endif()

  endif()



  if(OPENMP_RUNTIME STREQUAL "INTEL")

    # Find Intel libraries.

    find_library(IOMP5_LIBRARY iomp5 libiomp5md PATHS

      ${INTEL_ROOT}/lib

      ${INTEL_ROOT}/lib/intel64

      ${INTEL_ROOT}/compiler/lib/intel64

      ${INTEL_ROOT}/oneAPI/compiler/latest/windows/compiler/lib/intel64_win

      ${INTEL_ROOT}/oneapi/compiler/latest/linux/compiler/lib/intel64_lin

      ${INTEL_ROOT}/oneapi/compiler/latest/mac/compiler/lib

      )

    if(IOMP5_LIBRARY)

      list(APPEND LIBRARIES ${IOMP5_LIBRARY})

      message(STATUS "Using OpenMP: ${IOMP5_LIBRARY}")

    else()

      message(FATAL_ERROR "Intel OpenMP runtime libiomp5 not found")

    endif()

    if(WIN32)

      set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /nodefaultlib:vcomp")

      set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /nodefaultlib:vcomp")

    endif()

  elseif(OPENMP_RUNTIME STREQUAL "COMP")

    if(OpenMP_CXX_FOUND)

      list(APPEND LIBRARIES ${OpenMP_CXX_LIBRARIES})

      message(STATUS "Using OpenMP: ${OpenMP_CXX_LIBRARIES}")

    else()

      message(FATAL_ERROR "OpenMP not found")

    endif()

  else()

    message(FATAL_ERROR "Invalid OpenMP runtime ${OPENMP_RUNTIME}")

  endif()

endif()

```

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