[NDS32] We need to make sure it is NOT a variadic function so that some v3push/v3pop...

[NDS32] We need to make sure it is NOT a variadic function so that some v3push/v3pop preparation can be applied.

  -- The rationale of such avoidance is that the 'pop25' instruction also
     contains return behavior and we have no chance to further adjust stack
     pointer before returning to caller, which is very important to
     variadic function.
  -- So we do not setup v3push/v3pop (push25/pop25) information for a
     variadic function.  It will use normal stack push/pop instead.

	* config/nds32/nds32.c (nds32_compute_stack_frame): Do not use
	v3push/v3pop for variadic function.
	* config/nds32/nds32.md (prologue, epilogue): Likewise.

From-SVN: r214857