sem_ch3.adb (Analyze_Object_Declaration): Signal an error when an access to constant is used to initialize an access value.

    gcc/ada/
	* sem_ch3.adb (Analyze_Object_Declaration): Signal an error
	when an access to constant is used to initialize an access
	value.

    gcc/testsuite/
	* gnat.dg/specs/access_constant_decl.ads: New test.

From-SVN: r130677