[Ada] Issue info message on inlined subprograms in GNATprove mode

[Ada] Issue info message on inlined subprograms in GNATprove mode

Issue a positive message that inlining was performed in GNATprove mode,
when corresponding debug switch -gnatd_f is set.

2018-09-26  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* errout.ads: Update comment for insertion character '?'.
	* inline.adb: Use simple insertion character '?' for GNATprove
	info messages.
	* sem_res.adb (Resolve_Call): Issue an info message on inlining
	in GNATprove mode.

From-SVN: r264633