[Ada] Further evaluation of type bounds in GNATprove mode

[Ada] Further evaluation of type bounds in GNATprove mode

Some static bounds of types are not recognized and evaluated as such in the
semantic analysis phase of the frontend, which leads to incomplete information
in GNATprove. Fix that in the GNATprove mode only, as this is not needed when
full expansion is used.

There is no impact on compilation.

2018-05-28  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* sem_res.adb (Resolve_Range): Re-resolve the low bound of a range in
	GNATprove mode, as the order of resolution (low then high) means that
	all the information is not available when resolving the low bound the
	first time.

From-SVN: r260816