[Ada] Crash on conversion in branch of if-expression

[Ada] Crash on conversion in branch of if-expression

2019-12-16  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* checks.adb (Apply_Float_Conversion_Check): Use node of type
	conversion and not its parent, when inserting the declaration
	for the temporary that hold the result of the conversion.
	Previously the declaration was inserted above the parent of the
	conversion, apparently as a small optimization for the
	subsequent traversal in Insert_Actions.  Unfortunately a similar
	optimization takes place in Insert_Actions, assuming that the
	insertion point must be above the expression that creates the
	actions to insert.  This is not correct in the presence of
	conditional expressions (i.e.  since Ada2012), where the
	insertion must be in the list of actions attached to the current
	alternative.

From-SVN: r279422