exp_utils.ads, [...] (Find_Optional_Prim_Op): New interface to return Empty when...

exp_utils.ads, [...] (Find_Optional_Prim_Op): New interface to return Empty when not found...

2015-05-22  Bob Duff  <duff@adacore.com>

	* exp_utils.ads, exp_utils.adb (Find_Optional_Prim_Op): New
	interface to return Empty when not found, so we can avoid handling
	Program_Error in that case.
	(Find_Prim_Op): Fix latent bug: raise Program_Error when there are no
	primitives.
	* exp_ch7.adb, sem_util.adb: Use Find_Optional_Prim_Op when the
	code is expecting Empty.
	* sem_ch8.adb: Use Find_Optional_Prim_Op to avoid handling
	Program_Error.

From-SVN: r223541