# Translate a yes/no variable to the presence of a given string in a
# variable.
#
# Usage:
#   translate_flag(is_set flag_name var_name)
#
# If is_set is true, sets ${var_name} to ${flag_name}. Otherwise,
# unsets ${var_name}.
function(translate_flag is_set flag_name var_name)
  if(${is_set})
    set("${var_name}" "${flag_name}" PARENT_SCOPE)
  else()
    set("${var_name}" "" PARENT_SCOPE)
  endif()
endfunction()

macro(translate_flags prefix options)
  foreach(var ${options})
    translate_flag("${${prefix}_${var}}" "${var}" "${prefix}_${var}_keyword")
  endforeach()
endmacro()