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

test/asm/const-zero.err

@@ -0,0 +1,3 @@
+error: const-zero.asm(21) -> const-zero.asm::test_or(14):
+    Expected constant expression: PC is not constant at assembly time
+error: Assembly aborted (1 error)!

test/asm/const-zero.out

@@ -0,0 +1,6 @@
+What do you get if you multiply six by seven?
+Life, the Universe, and Everything!
+Where are we?
+Here we are!
+$0
+$0

test/asm/isconst.asm

@@ -6,7 +6,7 @@ MACRO test_expr
 
 	DEF IS_CONST = ISCONST(\1)
 	PRINTLN "Test #{d:TEST_NUM}: ISCONST reports {IS_CONST}"
-	IF (\1) || 1 ; Only test if the expression can be evaluated
+	IF (\1) || IS_CONST ; Only test if the expression can be evaluated
 		WARN "Test #{d:TEST_NUM}: Compile-time constant"
 	ENDC
 ENDM