ctkBlockSetCMakeOSXVariables - MacOSX 10.7, 10.6 and 10.5 are now considered

* Instead of hardcoding only one version of macosx, the macro
test if 10.7, 10.6 and then 10.5 exists.

* Waiting universal binaries are supported. It will complain
if multiple architectures are specified

* Thanks to Dr Hans J. Johnson from UCLA for its contribution

CMake/ctkBlockSetCMakeOSXVariables.cmake

@@ -28,15 +28,45 @@
 
 # Note: Change architecture *before* any enable_language() or project()
 #       calls so that it's set properly to detect 64-bit-ness...
-#       Currently, we default to 10.5. Obviously this may need to be re-evaluated when Lion comes out.
 #
 if(APPLE)
-  if(NOT CMAKE_OSX_DEPLOYMENT_TARGET OR "${CMAKE_OSX_DEPLOYMENT_TARGET}" STREQUAL "")
-    set(CMAKE_OSX_ARCHITECTURES "x86_64" CACHE STRING "force build for 64-bit Leopard" FORCE)
-    set(CMAKE_OSX_DEPLOYMENT_TARGET "10.5" CACHE STRING "force build for 64-bit Leopard" FORCE)
-    set(CMAKE_OSX_SYSROOT "/Developer/SDKs/MacOSX10.5.sdk" CACHE PATH "force build for 64-bit Leopard" FORCE)
+
+  # Waiting universal binaries are supported and tested, complain if
+  # multiple architectures are specified.
+  if(NOT "${CMAKE_OSX_ARCHITECTURES}" STREQUAL "")
+    list(LENGTH CMAKE_OSX_ARCHITECTURES arch_count)
+    if(arch_count GREATER 1)
+      message(FATAL_ERROR "error: Only one value (i386 or x86_64) should be associated with CMAKE_OSX_ARCHITECTURES.")
+    endif()
   endif()
 
+  # See CMake/Modules/Platform/Darwin.cmake)
+  #   8.x == Mac OSX 10.4 (Tiger)
+  #   9.x == Mac OSX 10.5 (Leopard)
+  #  10.x == Mac OSX 10.6 (Snow Leopard)
+  #  10.x == Mac OSX 10.7 (Lion)
+  set(OSX_SDK_104_NAME "Tiger")
+  set(OSX_SDK_105_NAME "Leopard")
+  set(OSX_SDK_106_NAME "Snow Leopard")
+
+  set(SDK_VERSIONS_TO_CHECK 10.7 10.6 10.5)
+  foreach(SDK_VERSION ${SDK_VERSIONS_TO_CHECK})
+    if(NOT CMAKE_OSX_DEPLOYMENT_TARGET OR "${CMAKE_OSX_DEPLOYMENT_TARGET}" STREQUAL "")
+      set(TEST_OSX_SYSROOT "/Developer/SDKs/MacOSX${SDK_VERSION}.sdk")
+      if(EXISTS "${TEST_OSX_SYSROOT}")
+        # Retrieve OSX target name
+        string(REPLACE "." "" sdk_version_no_dot ${SDK_VERSION})
+        set(OSX_NAME ${OSX_SDK_${sdk_version_no_dot}_NAME})
+        set(CMAKE_OSX_ARCHITECTURES "x86_64" CACHE STRING "Force build for 64-bit ${OSX_NAME}." FORCE)
+        set(CMAKE_OSX_DEPLOYMENT_TARGET "${SDK_VERSION}" CACHE STRING "Force build for 64-bit ${OSX_NAME}." FORCE)
+        set(CMAKE_OSX_SYSROOT "${TEST_OSX_SYSROOT}" CACHE PATH "Force build for 64-bit ${OSX_NAME}." FORCE)
+        message(STATUS "Setting OSX_ARCHITECTURES to '${CMAKE_OSX_ARCHITECTURES}' as none was specified.")
+        message(STATUS "Setting OSX_DEPLOYMENT_TARGET to '${SDK_VERSION}' as none was specified.")
+        message(STATUS "Setting OSX_SYSROOT to '${TEST_OSX_SYSROOT}' as none was specified.")
+      endif()
+    endif()
+  endforeach()
+
   if(NOT "${CMAKE_OSX_SYSROOT}" STREQUAL "")
     if(NOT EXISTS "${CMAKE_OSX_SYSROOT}")
       message(FATAL_ERROR "error: CMAKE_OSX_SYSROOT='${CMAKE_OSX_SYSROOT}' does not exist")