[Ada] Set Etype on rewriteen Max_Queue_Length expressions

[Ada] Set Etype on rewriteen Max_Queue_Length expressions

Rewriting of Max_Queue_Length expression into N_Integer_Literal should probably
be done in expansion and not in analysis, but anyway it should not strip the
expression from its Etype because backends (e.g. GNATprove) expect that Etype
to be present.

No frontend test is provided, because GNAT doesn't care about the missing
Etype decoration. This patch allows to simplify AST processing in GNATprove.

2018-05-31  Piotr Trojanek  <trojanek@adacore.com>

gcc/ada/

	* sem_prag.adb (Analyze_Pragma): Set Etype on the rewritten
	Max_Queue_Length expression.

From-SVN: r261002