[Ada] Representation clause for derived enumeration type is mishandled

[Ada] Representation clause for derived enumeration type is mishandled

This patch fixes an old-standing problem with premature freezing. When a
derived type declaration includes a constraint, we generate a subtype
declaration of an anonymous base type, with the constraint given in the
original type declaration, Conceptually, the bounds are converted to the
new base type, and this conversion freezes (prematurely) that base type,
when the bounds are simply literals.  As a result, a representation
clause for the derived type is then rejected or ignared. This procedure
recognizes the simple case of literal bounds in derived enumeration type
declarations, which allows us to indicate that the conversions are not
freeze points, and the subsequent representation clause can be accepted.

2019-08-19  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch3.adb (Derived_Enumeration_Type): Do no freeze anonymous
	base type if the bounds in the derived type declaration are
	literals of the type.

gcc/testsuite/

	* gnat.dg/rep_clause9.adb: New testcase.

From-SVN: r274641