[Ada] Crash on aggregate with dscriminant in if-expression as default

[Ada] Crash on aggregate with dscriminant in if-expression as default

This patch fixes a crash on a an aggregate for a discriminated type,
when a component of the aggregate is also a discriminated type
constrained by a discriminant of the enclosing object, and the default
value for the component is a conditional expression that includes
references to that outer discriminant.

2019-09-18  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_aggr.adb (Expand_Record_Aggregate, Rewrite_Discriminant):
	After rewriting a reference to an outer discriminant as a
	selected component of the enclosing object, analyze the selected
	component to ensure that the entity of the selector name is
	properly set. This is necessary when the aggregate appears
	within an expression that may have been analyzed already.

gcc/testsuite/

	* gnat.dg/discr58.adb: New testcase.

From-SVN: r275862