sem_prag.adb (Analyze_Pragma, [...]): Do not crash on illegal unchecked union that...

sem_prag.adb (Analyze_Pragma, [...]): Do not crash on illegal unchecked union that is a null record.

2012-06-12  Thomas Quinot  <quinot@adacore.com>

	* sem_prag.adb (Analyze_Pragma, case Unchecked_Union): Do
	not crash on illegal unchecked union that is a null record.

2012-06-12  Thomas Quinot  <quinot@adacore.com>

	* exp_ch4.adb (Has_Inferable_Discriminants): Reorganize code to
	treat implicit dereferences with a constrained unchecked union
	nominal subtype as having inferable discriminants.

From-SVN: r188437