Default EbsdLib_USE_GHC_FILESYSTEM=OFF. Warn on too old of macOS systems

Signed-off-by: Michael Jackson <mike.jackson@bluequartz.net>

CMakeLists.txt

@@ -104,18 +104,16 @@ if(APPLE)
   exec_program(uname ARGS -v  OUTPUT_VARIABLE DARWIN_VERSION)
   string(REGEX MATCH "[0-9]+" DARWIN_VERSION ${DARWIN_VERSION})
   if(DARWIN_VERSION VERSION_LESS 19)
-    set(EbsdLib_USE_GHC_FILESYSTEM ON)
-  endif()
-  if(CMAKE_OSX_DEPLOYMENT_TARGET VERSION_LESS 10.15)
-    set(EbsdLib_USE_GHC_FILESYSTEM ON)
+    message(STATUS "The current macOS System is too old to compile and will fail. Please set the EbsdLib_USE_GHC_FILESYSTEM=ON variable to allow Ebsdlib to compile")
   endif()
+  message(STATUS "EbsdLib: DARWIN_VERSION ${DARWIN_VERSION}")
+  message(STATUS "EbsdLib: CMAKE_OSX_DEPLOYMENT_TARGET: ${CMAKE_OSX_DEPLOYMENT_TARGET}")
 endif()
 if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0)
   set(EbsdLib_USE_GHC_FILESYSTEM ON)
 endif()
 
-message(STATUS "EbsdLib: DARWIN_VERSION ${DARWIN_VERSION}")
-message(STATUS "EbsdLib: CMAKE_OSX_DEPLOYMENT_TARGET: ${CMAKE_OSX_DEPLOYMENT_TARGET}")
+
 message(STATUS "EbsdLib: EbsdLib_USE_GHC_FILESYSTEM: ${EbsdLib_USE_GHC_FILESYSTEM}")
 
 if(EbsdLib_USE_GHC_FILESYSTEM)