[Ada] Hang on expansion of library-level instantiation

[Ada] Hang on expansion of library-level instantiation

This patch fixes an issue whereby instantiation of a generic at the
library-level may cause a hang or crash during compilation due to
inappropriate expansion of generic actuals.

2019-07-04  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* sem_ch12.adb (Perform_Appropriate_Analysis): Added for
	selecting which type of analysis based on wheither the
	instantiation is a generic at the library-level. In which case
	expansion during analysis.
	(Preanalyze_Actuals): Modify calls to Analyze to use the new
	routine.

gcc/testsuite/

	* gnat.dg/generic_inst4.adb, gnat.dg/generic_inst4_gen.ads,
	gnat.dg/generic_inst4_inst.ads, gnat.dg/generic_inst4_typ.ads:
	New testcase.

From-SVN: r273054