[Ada] Spurious elaboration issue due to inlining

[Ada] Spurious elaboration issue due to inlining

This patch ensures that the full compilation context is captured prior
to package or subprogram instantiation/inlining and restored after the
action takes place.

2018-09-26  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* sem_ch12.adb (Instantiate_Package_Body): Capture and restore
	the full compilation context.
	(Instantiate_Subprogram_Body): Capture and restore the full
	compilation context.

gcc/testsuite/

	* gnat.dg/elab7.adb, gnat.dg/elab7_pkg1.adb,
	gnat.dg/elab7_pkg1.ads, gnat.dg/elab7_pkg2.adb,
	gnat.dg/elab7_pkg2.ads: New testcase.

From-SVN: r264630