[Ada] Fix internal error on renaming of equality for record type

[Ada] Fix internal error on renaming of equality for record type

This adjusts the previous change to the cases where the array type is not
yet frozen and, therefore, where Size_Depends_On_Discriminant is not yet
computed, by doing the computation manually.

2018-05-28  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* exp_ch4.adb (Expand_Composite_Equality): Compute whether the size
	depends on a discriminant manually instead of using the predicate
	Size_Depends_On_Discriminant in the array type case.

gcc/testsuite/

	* gnat.dg/renaming12.adb, gnat.dg/renaming12.ads: New testcase.

From-SVN: r260839