Do not try to link to librt.so on Android

[NPellet]

clFFT seems cross-compilable for android.
The only error I encountered was in the makefile of startTimer:

if( UNIX AND NOT APPLE )
	# This library dependency is brought in by the high precision timer available in linux
	target_link_libraries( StatTimer -lrt )
endif( )

Should be

if( UNIX AND NOT APPLE AND NOT ANDROID )
	# This library dependency is brought in by the high precision timer available in linux
        # In Android, there's no need to link against rt
	target_link_libraries( StatTimer -lrt )
endif( )

PR needed ?