Generate more efficient code for certain subtractions.

This affects 16-bit subtractions where where only the left operand is "complex" (i.e. most things other than constants and simple loads). They were using an unnecessarily complicated code path suitable for the case where both operands are complex.

Gen.pas

@@ -6998,7 +6998,7 @@ procedure GenTree {op: icptr};
    { Generate code for a pc_sbi					}
    
    begin {GenSbi}
-   if Complex(op^.left) or Complex(op^.right) then begin
+   if Complex(op^.right) then begin
       GenTree(op^.right);
       if Complex(op^.left) then begin
 	 GenImplied(m_pha);