[Ada] Crash on interface equality covered by a renaming declaration

[Ada] Crash on interface equality covered by a renaming declaration

The frontend crashes processing a tagged type that implements an
interface which has an equality primitive (that is, "=") and covers such
primitive by means of a renaming declaration.

2018-11-14  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* exp_disp.adb (Expand_Interface_Thunk): Extend handling of
	renamings of the predefined equality primitive.
	(Make_Secondary_DT): When calling Expand_Interface_Thunk() pass
	it the primitive, instead of its Ultimate_Alias; required to
	allow the called routine to identify renamings of the predefined
	equality operation.

gcc/testsuite/

	* gnat.dg/equal5.adb, gnat.dg/equal5.ads: New testcase.

From-SVN: r266130