ada: sem_ch13.adb: accept VADS inline asm in Relaxed RM Semantics mode

ada: sem_ch13.adb: accept VADS inline asm in Relaxed RM Semantics mode

VADS inline assembly works by using a qualified expression for one of
the types defined in the Machine_Code package, e.g.

   procedure P is
   begin
      code_2'(INSTR, OPERAND1, OPERAND2);
   end y;

This is different from GNAT's own inline assembly machinery, which
instead expects a call to Machine_Code.ASM with a set of
differently-typed arguments.

This incompatibility is preventing GNATSAS' GNAT-Warnings engine from
analyzing VADS code, hence we adapt sem_ch13.adb to not fail on such
constructs when GNAT is running under both Check_Semantics_Only_Mode and
Relaxed_RM_Semantics mode.

gcc/ada/ChangeLog:

	* sem_ch13.adb (Analyze_Code_Statement): Do not emit error
	message when only checking relaxed semantics.