message: remove openmpi-simd flag if compiler lacks support for it
diff: ## Copyright 2009-2020 Intel Corporation
  ## SPDX-License-Identifier: Apache-2.0
  +include(CheckCXXCompilerFlag)
  +
  set(OIDN_C_CXX_FLAGS)
  set(OIDN_C_CXX_FLAGS_RELEASE)
  set(OIDN_C_CXX_FLAGS_DEBUG)
  @@ -142,8 +144,11 @@ if(WIN32)
  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Intel")
  append(OIDN_C_CXX_FLAGS "-qopenmp-simd")
  else()
  + check_cxx_compiler_flag(-fopenmp-simd compiler-openmp-simd-support)
  + if(compiler-openmp-simd-support)
  append(OIDN_C_CXX_FLAGS "-fopenmp-simd")
  endif()
  +endif()
  ## -----------------------------------------------------------------------------
  ## Secure Development Lifecycle (SDL)
  