[Ada] Do not suppress checks in instances of internal generics

[Ada] Do not suppress checks in instances of internal generics

This patch removes suppression of checks in nested instances of internal
packages. No test.

This was inconsistent: only for packages, not for subprograms. Only for
nested instantiations, not library level ones. Not for GNAT units.

Furthermore, the user should have control via pragma Suppress or
switches.

Furthermore, without this change, there could be missing tampering
checks in Ada.Containers.

2019-08-12  Bob Duff  <duff@adacore.com>

gcc/ada/

	* sem_ch12.adb (Instantiate_Package_Body): Remove suppression of
	checks in instances of internal units.
	* sem_ch6.adb (Analyze_Function_Return): Do not generate a
	constraint check on an extended_return_statement if the subtype
	of the return object in the statement is identical to the return
	subtype of the function.

From-SVN: r274302