[Ada] Defer processing of unknown CTW/E conditions to the back end

[Ada] Defer processing of unknown CTW/E conditions to the back end

2019-08-14  Bob Duff  <duff@adacore.com>

gcc/ada/

	* sem_prag.adb (Process_Compile_Time_Warning_Or_Error): Defer
	processing to the back end in all cases where the pragma's
	condition is not known at compile time during the front end
	(except in generics), as opposed to detecting 'Size attributes
	and the like. This ensures that we take advantage of whatever
	can be compile-time known after running the back end, as opposed
	to having the front end guess what the back end can do.  Remove
	a little duplicated code at the call site.
	* gnat1drv.adb (Post_Compilation_Validation_Checks): Unlock the
	Elists while in Validate_Compile_Time_Warning_Errors, because it
	does analysis and name resolution, which sometimes involves
	adding Elists.

From-SVN: r274466