Restore blue-painting of macro arg expansions to prevent recursion

test/asm/macro-arg-recursion.asm

@@ -0,0 +1,6 @@
+MACRO m
+	def x = (\1) * 2
+	println "{d:x}"
+ENDM
+	m 5       ; prints 10
+	m \\2, 6  ; should not prints 12

test/asm/macro-arg-recursion.err

@@ -0,0 +1,3 @@
+error: macro-arg-recursion.asm(6) -> macro-arg-recursion.asm::m(2):
+    Begun line continuation, but encountered character '2'
+Assembly aborted with 1 error!

test/asm/macro-arg-recursion.out

@@ -0,0 +1,2 @@
+10
+4