[Ada] Fix internal error on inlined subprogram instance

[Ada] Fix internal error on inlined subprogram instance

This fixes a long-standing oddity in the procedure analyzing the
instantiation of a generic subprogram, which would set the
Is_Generic_Instance flag on the enclosing package generated for the
instantiation but only to reset it a few lines below.  Now this flag is
relied upon by the machinery which computes the set of public entities
to be exposed by a package.

2019-08-14  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* sem_ch12.adb (Analyze_Instance_And_Renamings): Do not reset
	the Is_Generic_Instance flag previously set on the package
	generated for the instantiation of a generic subprogram.

gcc/testsuite/

	* gnat.dg/generic_inst11.adb, gnat.dg/generic_inst11_pkg.adb,
	gnat.dg/generic_inst11_pkg.ads: New testcase.

From-SVN: r274457