[Ada] Deep copy operands of membership operations for unnesting

[Ada] Deep copy operands of membership operations for unnesting

2018-07-16  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_ch4.adb (Expand_Set_Membership): Use New_Copy_Tree to perform a
	deep copy of the left operand when building each conjuct of the
	expanded membership operation, to avoid sharing nodes between them.
	This sharing interferes with the unnesting machinery and is generally
	undesirable.

From-SVN: r262727