Don't overwrite the deployment target that MacPorts sets.
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -37,9 +37,6 @@ endif()
 # Always build with position-independent code (-fPIC)
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
-set(CMAKE_OSX_DEPLOYMENT_TARGET 10.9 CACHE STRING 
-    "make for this OS version or higher")
-
 # PM_ACTUAL_LIB_NAME is in this scope -- see pm_common/CMakeLists.txt
 # PM_NEEDED_LIBS is in this scope -- see pm_common/CMakeLists.txt