This patch fixds a spurious error report on a prefixed call where the
operation is a private overriding of a visible operation, and the operation
has various overloadings in the visible and private parts.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

2017-12-05  Ed Schonberg  <schonberg@adacore.com>

	* sem_ch4.adb (Is_Private_Overriding): If the candidate private
	subprogram is overloaded, scan the list of homonyms in the same
	scope, to find the inherited operation that may be overridden
	by the candidate.
	* exp_ch11.adb, exp_ch7.adb: Minor reformatting.

gcc/testsuite/

2017-12-05  Ed Schonberg  <schonberg@adacore.com>

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