Make the comma after assert warn/fail/fatal optional (#2160)

Co-authored-by: Eldred Habert <[email protected]>

test/asm/assert-comma.asm

@@ -0,0 +1,24 @@
+def n = 0
+for i_type, 5
+	redef type equs strslice("     warn fail warn,fail,", i_type * 5, (i_type + 1) * 5)
+	for i_message, 2
+		redef message equs ", \"hello {d:n}\""
+		redef message equs strslice(#message, 0, i_message * strlen(#message))
+		for cond, 2
+			redef line equs "assert {type} {cond} {message}"
+			println "[static_]{line}"
+			{line}
+			static_{line}
+			def n += 1
+		endr
+	endr
+endr
+
+println "[static_]assert fatal..."
+assert fatal 1
+assert fatal 1, "goodbye 0"
+static_assert fatal 1
+static_assert fatal 1, "goodbye 0"
+
+assert fatal 0
+assert fatal 0, "goodbye 1" ; not reached