[Ada] Use type conversion when inlining may trigger a run-time check

[Ada] Use type conversion when inlining may trigger a run-time check

In the frontend inlining used in GNATprove, inlining of a return statement
was using an unchecked type conversion, which could cause a necessary
run-time check on the conversion to be skipped. Now fixed.

There is no impact on compilation.

2018-05-21  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* inline.adb (Expand_Inlined_Call.Process_Formals): Use a type
	conversion instead of an unchecked type conversion when inlining a
	return statement, unless type qualification is required (for character
	and string literal) or no check can result from the conversion (for
	access types).
	* opt.ads: Update comment.

From-SVN: r260458