[Ada] Spurious undefined symbol with nested call to expression function

[Ada] Spurious undefined symbol with nested call to expression function

2020-06-16  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* freeze.adb: (Freeze_Expression, In_Expanded_Body): Treat the
	generated body of an expression function like other bodies
	generated during expansion (e.g. stream subprograms) so that
	those bodies are not treated as freezing points. Handle properly
	other global references in such completions.