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The foreach() construct can be used in four different ways:

• foreach(loop_var arg1 arg2 ...): Where a loop variable and an explicit list of items are provided. This form was used when printing the compiler flag sets for the items in sources_with_lower_optimization. Note that if the list of items is in a variable, it has to be explicitly expanded; that is, ${sources_with_lower_optimization} has to be passed as an argument.
• As a loop over integer numbers by specifying a range, such as foreach(loop_var RANGE total) or alternatively
  foreach(loop_var RANGE start stop [step]).
• As a loop over list-valued variables, such as foreach(loop_var IN LISTS [list1 [...]]). The arguments are interpreted as lists and their contents automatically expanded accordingly.
• As a loop over items, such as foreach(loop_var IN ITEMS [item1 [...]]). The contents of the arguments are not expanded.