BUG: Fix careless typo that only caused test failures on clean builds...

Modules/Platform/Darwin.cmake

@@ -158,7 +158,7 @@ SET(CMAKE_OSX_ARCHITECTURES_DEFAULT ${_CMAKE_OSX_MACHINE})
 IF(NOT "$ENV{CMAKE_OSX_ARCHITECTURES}" STREQUAL "")
   SET(CMAKE_OSX_ARCHITECTURES_VALUE "$ENV{CMAKE_OSX_ARCHITECTURES}")
 ELSE(NOT "$ENV{CMAKE_OSX_ARCHITECTURES}" STREQUAL "")
-  SET(CMAKE_OSX_ARCHITECTURES_VALUE "{CMAKE_OSX_ARCHITECTURES_DEFAULT}")
+  SET(CMAKE_OSX_ARCHITECTURES_VALUE "${CMAKE_OSX_ARCHITECTURES_DEFAULT}")
 ENDIF(NOT "$ENV{CMAKE_OSX_ARCHITECTURES}" STREQUAL "")
 
 # now put _CMAKE_OSX_MACHINE into the cache