[Ada] Regression in partial compilation of RCI units

[Ada] Regression in partial compilation of RCI units

This patch fixes an issue whereby the compilation of partial sources
(packages without bodies that require them) would not occur when said
sources were remote call interfaces. This is required because such
interfaces may have bodies that only exist on the server side or vice
versa

2018-09-26  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* lib-writ.adb, lib-writ.ads (Write_With_Lines): Add
	documentation and an extra conditional check for RCI units so
	that generated ali files will list the spec only instead of a
	body when a body is not found.

From-SVN: r264608