macro(filter_list inlist regex)
	set(outlist "")
	foreach(item ${${inlist}})
		if(NOT ${outitem} ${item} MATCHES ${regex})
			list(APPEND outlist ${item})
		endif()
	endforeach()
	set(${inlist} ${outlist})
endmacro()

set(mylist FILTER_THIS_BIT DO_NOT_FILTER_THIS thisisanitem FILTER_THIS_THING)
message("mylist was: ${mylist}")
filter_list(mylist "^FILTER_THIS_.+")
message("mylist is: ${mylist}")