[Ada] Do not issue by default info messages for inlining in GNATprove

[Ada] Do not issue by default info messages for inlining in GNATprove

Info messages about lack of inlining for analysis in GNATprove may be
confusing to users. They are now only issued when GNATprove is called
with switch --info, which it passes on to gnat2why with switch -gnatd_f.

There is no effect on compilation.

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

gcc/ada/

	* debug.adb: Add use for -gnatd_f switch.
	* inline.adb (Cannot_Inline): Only issue info message for
	failure to inline in GNATprove mode when switch -gnatd_f is
	used.

From-SVN: r264629