kaffe-0.8.2 m68k JIT bug (and fix)

[Esa Salonen]

If M68K_RETURN_REF is not REG_a0 but the more usual d0 register,
then in some cases jit generated code is like:

	moveal fp@(-20),a2
	moveal a2,a4
	movel a0,d0    <-- shoud be a4,d0
	unlk fp
	rts

a0 was some random value, and method returned that.

I assume that with  M68K_RETURN_REF a0 you get something like
	moveal fp@(-20),a2
	moveal a2,a4
	moveal a4,a0
	movel a0,d0
	unlk fp
	rts

which works but movel a0,d0 is unnecessary, and could be easily eliminated

After following fix generated code looks like this:
(When M68K_RETURN_REF is d0)

	moveal fp@(-20),a2
	moveal a2,a4
	movel a4,d0
	unlk fp
	rts

This works OK but I just wonder how those numerous copy instructions could be
optimized away.

*** kaffe-0.8.2/config/m68k/jit-m68k.def~	Sun Feb 23 19:01:11 1997
--- kaffe-0.8.2/config/m68k/jit-m68k.def	Wed Mar  5 12:04:09 1997
***************
*** 2244,2250 ****
  	}
  
  	if (r != REG_d0) {
! 		op_movel_ad(REG_a0, REG_d0);
  	}
  }
  
--- 2244,2251 ----
  	}
  
  	if (r != REG_d0) {
! 		op_movel_ad(r, REG_d0);
! 	/* 	op_movel_ad(REG_a0, REG_d0); bug! */
  	}
  }