Allow binary AND to be sometimes constant (#976)

test/asm/const-and.asm

@@ -0,0 +1,17 @@
+
+	println @ & 0 ; This should produce an error, but not crash
+
+SECTION "Test", ROM0,ALIGN[4,2]
+
+	ds 40
+Aligned:
+
+	println Aligned & $0f
+	println ~$fffc & Aligned
+	println Aligned & $1f ; Not constant
+	println @ & $0f
+
+SECTION "Unaligned", ROM0
+
+	println @ & 0
+	println @ & 1 ; Nope

test/asm/const-and.err

@@ -0,0 +1,7 @@
+error: const-and.asm(2):
+    PC has no value outside a section
+error: const-and.asm(11):
+    Expected constant expression: 'Aligned' is not constant at assembly time
+error: const-and.asm(17):
+    Expected constant expression: PC is not constant at assembly time
+error: Assembly aborted (3 errors)!

test/asm/const-and.out

@@ -0,0 +1,7 @@
+$0
+$A
+$A
+$0
+$A
+$0
+$0

test/link/assert.asm

@@ -1,11 +1,9 @@
 
 SECTION "test", ROM0
 
-	ds 123
-
 FloatingBase:
-	assert WARN, FloatingBase & 0, "Worry about me, but not too much."
-	assert FAIL, FloatingBase & 0, "Okay, this is getting serious!"
-	assert FATAL, FloatingBase & 0, "It all ends now."
-	assert FAIL, FloatingBase & 0, "Not even time to roll credits!"
+	assert WARN, FloatingBase, "Worry about me, but not too much."
+	assert FAIL, FloatingBase, "Okay, this is getting serious!"
+	assert FATAL, FloatingBase, "It all ends now."
+	assert FAIL, FloatingBase, "Not even time to roll credits!"
 	assert WARN, 0, "Still can finish the film, though!"

test/link/assert.out

@@ -1,4 +1,4 @@
-warning: assert.asm(7): Worry about me, but not too much.
-error: assert.asm(8): Okay, this is getting serious!
-FATAL: assert.asm(9): It all ends now.
+warning: assert.asm(5): Worry about me, but not too much.
+error: assert.asm(6): Okay, this is getting serious!
+FATAL: assert.asm(7): It all ends now.
 Linking aborted after 2 errors