[Ada] Missing warning for unreferenced formals in expression functions

[Ada] Missing warning for unreferenced formals in expression functions

This patch fixes an issue whereby the compiler failed to properly warn against
unreferenced formal parameters when analyzing expression functions.

2018-05-22  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* sem_ch6.adb (Analyze_Expression_Function): Propagate flags from the
	original function spec into the generated function spec due to
	expansion of expression functions during analysis.
	(Analyze_Subprogram_Body_Helper): Modify check on formal parameter
	references from the body to the subprogram spec in the case of
	expression functions because of inconsistances related to having a
	generated body.
	* libgnarl/s-osinte__android.ads: Flag parameters as unused.
	* libgnarl/s-osinte__lynxos178e.ads: Likewise.
	* libgnarl/s-osinte__qnx.adb: Likewise.
	* libgnarl/s-osinte__qnx.ads: Likewise.

gcc/testsuite/

	* gnat.dg/warn14.adb: New testcase.

From-SVN: r260535