[Ada] Incorrect source line range on subprogram body with contract

[Ada] Incorrect source line range on subprogram body with contract

2020-06-04  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sinput.adb (Sloc_Range): Ignore node in the tree if it appears
	in a unit different from that of the node whose Sloc range we
	are computing. This is necessary when computing the source range
	of a subprogram body whose declaration includes a pre- or
	postcondition, because declaration and body may appear in
	different units, and the expanded code for the body includes
	copies of the contract code.