checking exist is not required for cache variables

CMakeLists.txt

@@ -34,16 +34,12 @@ get_property(MIGRAPHX_GENERATOR_IS_MULTI_CONFIG GLOBAL PROPERTY GENERATOR_IS_MUL
 # This has to be initialized before the project() command appears
 # Set the default of CMAKE_BUILD_TYPE to be release, unless user specifies with -D.  MSVC_IDE does not use CMAKE_BUILD_TYPE
 if(NOT MIGRAPHX_GENERATOR_IS_MULTI_CONFIG)
-    if (NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE Release CACHE STRING
         "Choose the type of build, options are: None Debug Release RelWithDebInfo MinSizeRel.")
     set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS ${MIGRAPHX_CONFIGURATION_TYPES})
-    endif()
 else()
-    if (NOT CMAKE_CONFIGURATION_TYPES)
     set(CMAKE_CONFIGURATION_TYPES ${MIGRAPHX_CONFIGURATION_TYPES} CACHE STRING
         "Available build types (configurations) on multi-config generators")
-    endif()
 endif()
 
 if(NOT WIN32)