Add test for HIGH() and LOW()

It compares the results of the operators with the expected result if
doing the same thing manually.

Signed-off-by: Antonio Niño Díaz <antonio_nd@outlook.com>

test/link/high-low-b.asm

@@ -0,0 +1,18 @@
+SECTION "r0", ROM0[$0]
+ld a,a
+ld b,c
+ld c,b
+ld d,e
+ld e,d
+ld h,l
+ld l,h
+
+db ((label+$AB) >> 8) & $FF
+db (label+$AB) & $FF
+
+db ($1234 >> 8) & $FF
+db $1234 & $FF
+
+SECTION "o",OAM
+DS $10
+label: