Optimize loading constants

[ZERICO2005]

	ld	de, (ix - 30)
	ld	hl, (ix + 12)
	ld	iy, 12
	lea	bc, iy + 0
	ldir
	ld	de, (ix + 12)
	ld	iy, (ix - 27)
	lea	hl, iy + 0
	ld	bc, 12 ; can be changed to ld c, 12
	ldir
	lea	de, iy + 0
	ld	hl, (ix - 30)
	ld	bc, 12 ; can be changed to ld c, 12
	ldir

LDIR sets BC to 0, so the compiler can use this information to change ld bc, 12 to ld c, 12

	ld	hl, (ix + 21)
	ld	iy, 12
	lea	bc, iy + 0
	ldir
	ld	de, (ix + 21)
	ld	hl, (ix + 15)
	lea	bc, iy + 0 ; can be changed to ld c, 12
	ldir
	ld	de, (ix + 15)
	ld	hl, (ix - 33)
	lea	bc, iy + 0 ; can be changed to ld c, 12
	ldir

Similar thing here