ada: Improve handling of declare expressions in deferred-freezing contexts

ada: Improve handling of declare expressions in deferred-freezing contexts

In some cases where a declare expression occurs in a deferred-freezing
context (e.g., within the default value for a discriminant or for a formal
parameter, or within the expression of an expression function), the compiler
generates a bugbox.

gcc/ada/

	* sem_ch3.adb
	(Analyze_Object_Declaration): Do not perform expansion actions if
	In_Spec_Expression is true.