PKG: JIRA 975. use Darwin prefix for OSX

SuperBuild/CMake/External_package.cmake

@@ -22,12 +22,19 @@ endif()
 set(PACKAGE_NAME OTB)
 set(PACKAGE_LONG_NAME OrfeoToolBox)
 
-set(PACKAGE_ARCH Linux32)
+if(UNIX)
+  if(APPLE)
+    set(PACKAGE_PLATFORM_NAME "Darwin")
+  else()
+    set(PACKAGE_PLATFORM_NAME "Linux")
+  endif()
+endif()
+set(PACKAGE_ARCH 32)
 if(CMAKE_SIZEOF_VOID_P EQUAL 8)
-  set(PACKAGE_ARCH Linux64)
+  set(PACKAGE_ARCH 64)
 endif()
 
-set(ARCHIVE_NAME ${PACKAGE_NAME}-${PACKAGE_VERSION}-${PACKAGE_ARCH})
+set(ARCHIVE_NAME ${PACKAGE_NAME}-${PACKAGE_VERSION}-${PACKAGE_PLATFORM_NAME}${PACKAGE_ARCH})
 
 set(MAKESELF_SCRIPT ${CMAKE_BINARY_DIR}/PACKAGE-OTB/build/makeself.sh)