[Ada] Missing error on generic type with representation clause

[Ada] Missing error on generic type with representation clause

The compiler does not report an error on a generic type that has a
representation clause when its ultimate parent is not a generic formal.

2019-07-09  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* sem_ch13.adb (Rep_Item_Too_Early): Representation clauses are
	not allowed for a derivation of a generic type. Extend the
	current test to check that none of the parents is a generic
	type.

gcc/testsuite/

	* gnat.dg/rep_clause8.adb: New testcase.

From-SVN: r273283