[Ada] Spurious error on indexed call as prefix of a call

[Ada] Spurious error on indexed call as prefix of a call

This patch refines the handling of the well-known syntactic ambiguity created
by a function with defaulted parameters that returns an array, so that F (X)
may designate a call to the function, or an indexing of a parameterless call.
This patch handles the case where such a call is itself the prefix of another
call, and the function is a primitive operation invoked in prefix form.

2018-05-21  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch4.adb (Analyze_One_Call): Recognize complex cases where an
	indexed call originally in prefix forn is itself the prefix of a
	further call.

gcc/testsuite/

	* gnat.dg/array30.adb: New testcase.

From-SVN: r260461