[Ada] Ensure that Scan_Real result does not depend on trailing zeros

[Ada] Ensure that Scan_Real result does not depend on trailing zeros

Previous change in that procedure to handle overflow issues during
scanning removed the special handling for trailing zeros in the decimal
part. Beside the absence of overflow during scanning the special
handling of these zeros is still necessary.

2019-09-18  Nicolas Roche  <roche@adacore.com>

gcc/ada/

	* libgnat/s-valrea.adb (Scan_Integral_Digits): New procedure.
	(Scan_Decimal_Digits): New procedure.
	(As_Digit): New function.
	(Scan_Real): Use Scan_Integral_Digits and Scan_Decimal_Digits.

gcc/testsuite/

	* gnat.dg/float_value2.adb: New testcase.

From-SVN: r275849