Add more test coverage for RGBASM (#1256)

This also fixes two bugs: `-1 >>> 32` was -1 not 0, and `macro_FreeArgs` should have been called but wasn't.

test/asm/def-scoped.asm

@@ -0,0 +1,16 @@
+SECTION "test", ROM0
+
+; this is okay...
+Label:
+Label.local:
+
+; ...but these are not
+
+DEF n EQU 1
+DEF n.local EQU 2
+
+DEF x = 1
+DEF x.local = 2
+
+DEF s EQUS "..."
+DEF s.local EQUS "..."