[Ada] Spurious error on default parameter in protected operation

[Ada] Spurious error on default parameter in protected operation

This patch fixes a spurious compiler error on a call to a protected
operation whose profile includes a defaulted in-parameter that is a call
to another protected function of the same object.

2018-07-31  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_ch6.adb (Expand_Protected_Subprogram_Call): Handle
	properly a protected call that includes a default parameter that
	is a call to a protected function of the same type.

gcc/testsuite/

	* gnat.dg/prot5.adb, gnat.dg/prot5_pkg.adb,
	gnat.dg/prot5_pkg.ads: New testcase.

From-SVN: r263101