Fix detection of ghc_filesystem on macOS systems

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

CMakeLists.txt

@@ -99,17 +99,18 @@ endif()
 # Determine if we need the ghcFilesystem library
 #-------------------------------------------------------------------------------
 set(EbsdLib_USE_GHC_FILESYSTEM OFF)
-if(CMAKE_OSX_ARCHITECTURES STREQUAL "arm64")
-  set(EbsdLib_USE_GHC_FILESYSTEM OFF)
-elseif(APPLE AND CMAKE_OSX_DEPLOYMENT_TARGET VERSION_LESS 10.15)
-  set(EbsdLib_USE_GHC_FILESYSTEM ON)
-  if("${CMAKE_OSX_DEPLOYMENT_TARGET}" STREQUAL "")
-    message(WARNING "CMAKE_OSX_DEPLOYMENT_TARGET is empty. Assuming macOS deployment *OLDER* than 10.15 Catalina. This will require ghcFilesystem library.")
+
+if(APPLE)
+  exec_program(uname ARGS -v  OUTPUT_VARIABLE DARWIN_VERSION)
+  string(REGEX MATCH "[0-9]+" DARWIN_VERSION ${DARWIN_VERSION})
+  message(STATUS "DARWIN_VERSION ${DARWIN_VERSION}")
+  if(DARWIN_VERSION VERSION_LESS 19)
+    set(EbsdLib_USE_GHC_FILESYSTEM ON)
   endif()
 elseif(${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU" AND "${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0)
   set(EbsdLib_USE_GHC_FILESYSTEM ON)
 endif()
-
+message(STATUS "EbsdLib_USE_GHC_FILESYSTEM: ${EbsdLib_USE_GHC_FILESYSTEM}")
 if(EbsdLib_USE_GHC_FILESYSTEM)
   find_package(ghcFilesystem REQUIRED NAMES ghc_filesystem ghcFilesystem)
 endif()