message: Improve CMake backwards compatibility
  This changelist updates the CMakeLists.txt file in MaterialXTest to use patterns supported by earlier versions of CMake in addition to the latest version.
diff: +file(GLOB materialx_source "${CMAKE_CURRENT_SOURCE_DIR}/*.cpp")
  +file(GLOB materialx_headers "${CMAKE_CURRENT_SOURCE_DIR}/*.h*")
  +list(APPEND materialx_headers "${CMAKE_CURRENT_SOURCE_DIR}/Catch/catch.hpp")
  +
  +assign_source_group("Source Files" ${materialx_source})
  +assign_source_group("Header Files" ${materialx_headers})
  +
  set(MATERIALX_TEST_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}")
  # Discover all tests and allow them to be run in parallel (ctest -j20):
  @@ -15,22 +22,12 @@ function(add_tests _sources)
  endforeach()
  endfunction()
  -add_executable(MaterialXTest)
  +add_executable(MaterialXTest ${materialx_source} ${materialx_headers})
  target_include_directories( MaterialXTest PUBLIC
  ${EXTERNAL_INCLUDE_DIRS}
  ${CMAKE_CURRENT_SOURCE_DIR}/../)
  -file(GLOB materialx_source "${CMAKE_CURRENT_SOURCE_DIR}/*.cpp")
  -file(GLOB materialx_headers "${CMAKE_CURRENT_SOURCE_DIR}/*.h")
  -
  -list(APPEND materialx_headers "${CMAKE_CURRENT_SOURCE_DIR}/Catch/catch.hpp")
  -
  -assign_source_group("Source Files" ${materialx_source})
  -assign_source_group("Header Files" ${materialx_headers})
  -
  -target_sources(MaterialXTest PUBLIC ${materialx_source} ${materialx_headers})
  -
  add_subdirectory(MaterialXCore)
  target_link_libraries(MaterialXTest MaterialXCore)
  add_subdirectory(MaterialXFormat)
  