cmake fix broken OSX build: those openmp flags break OSX build, it might only work on other unixes that way

CMakeLists.txt

@@ -82,11 +82,11 @@ OPTION(WITH_INSTALL       "Install accompanying scripts and language files neede
 OPTION(WITH_OPENCOLLADA		"Enable OpenCollada Support (http://www.opencollada.org/)"	ON)
 
 # Unix defaults to OpenMP On
-IF (UNIX)
+IF(UNIX AND NOT APPLE)
 	OPTION(WITH_OPENMP        "Enable OpenMP (has to be supported by the compiler)" ON)
-ELSE(UNIX)
+ELSE()
 	OPTION(WITH_OPENMP        "Enable OpenMP (has to be supported by the compiler)" OFF)
-ENDIF(UNIX)
+ENDIF()
 
 IF (APPLE)
 	OPTION(WITH_COCOA	  "Use Cocoa framework instead of deprecated Carbon" ON)