To warn about infinite loops we detect variables referenced in loop exit
conditions. We handle references within boolean operators, i.e.
comparison and negation, which are likely to appear at the top level of
the condition (e.g. "X > 0"). However, we can easily handle all
operators, because they are likely to appear inside the condition (e.g.
"abs (X) > 0.0").

Cleanup related to a new restriction No_Uninitialized_Local_Scalars.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_warn.adb (Find_Var): Detect all operators; replace
	"condition" to "expression" in comments, because when this
	routine is called recursively it no longer examines the
	condition.
	(Is_Suspicious_Function_Name): Reduce scope of a local variable
	to avoid shadowing with a parameter of a nested
	Substring_Present function.