X && 0 and X & 0 are constant 0; X || 1 is constant 1 (#1399)

Fixes #977

test/asm/const-zero.asm

@@ -0,0 +1,29 @@
+MACRO test_and
+	if DEF(foo) && foo == 42
+		println "Life, the Universe, and Everything!"
+	else
+		println "What do you get if you multiply six by seven?"
+	endc
+ENDM
+	test_and
+	DEF foo = 42
+	test_and
+
+
+MACRO test_or
+	if DEF(DEBUG) || @ == $4567
+		println "Here we are!"
+	else
+		println "Where are we?"
+	endc
+ENDM
+	SECTION "Test OR", ROMX
+	test_or ; Not constant
+	DEF DEBUG EQU 1
+	test_or
+
+
+SECTION "Test arithmetic", ROM0
+Floating:
+	println Floating & 0
+	println 0 & Floating