ada: Warn about redundant parentheses inside unary operators

GNAT already emits a style warning when redundant parentheses appear inside
logical and short-circuit operators. A similar warning is now emitted for
unary operators as well.

gcc/ada/ChangeLog:

	* par-ch4.adb (P_Factor): Warn when the operand of a unary operator
	doesn't require parentheses.