Add more tests for RGBASM coverage

test/asm/warning-as-error.asm

@@ -0,0 +1,14 @@
+DEF n = -99 >> 1 ; -Wshift
+DEF n = 999_999_999_999 ; -Wlarge-constant
+
+MACRO test
+	WARN "warning or error?"
+ENDM
+
+test
+
+OPT Werror
+test
+
+OPT Wno-error
+test