[Ada] Fix inconsistent quoting in messages about compile-time errors

[Ada] Fix inconsistent quoting in messages about compile-time errors

gcc/ada/

	* exp_ch4.adb (Raise_Accessibility_Error): Move exception name
	to the message string; move << control characters to the end,
	for consistency.
	* sem_ch6.adb (Analyze_Function_Return): Likewise.
	* sem_util.adb (Compile_Time_Constraint_Error): Likewise.
	* gcc-interface/decl.c (gnat_to_gnu_entity): Remove quotes
	around Storage_Error.
	* gcc-interface/trans.c (gnat_to_gnu): Remove quotes around
	Constraint_Error.

gcc/testsuite/

	* gnat.dg/aggr26.adb: Update expected error message.