Clean up label generation

Only check for localness when we already know we have a local

test/asm/label-macro-arg.err

@@ -1,5 +1,5 @@
 ERROR: label-macro-arg.asm(44) -> label-macro-arg.asm::test_char(31):
-    Local label in main scope
+    Local label 'sizeof_.something' in main scope
 while expanding symbol "VAR_DEF"
 ERROR: label-macro-arg.asm(44) -> label-macro-arg.asm::test_char(31):
     syntax error

test/asm/sym-scope.asm

@@ -0,0 +1,21 @@
+SECTION "Scopes", ROM0
+
+; Neither of these should be created
+.tooSoon
+Nice.try
+
+Parent:
+.loc
+	dw Parent.loc ; This is what it should expand to
+Parent.explicit
+	dw .explicit ; This should expand to the above
+
+
+; None of the two locals below should manage to be created, being in the wrong scopes
+; Note however that `Parentheses` begins with `Parent`, which string checks may fail to handle
+
+Parentheses.check
+
+Parentheses:
+
+Parent.check

test/asm/sym-scope.err

@@ -0,0 +1,9 @@
+ERROR: sym-scope.asm(4):
+    Local label '.tooSoon' in main scope
+ERROR: sym-scope.asm(5):
+    Local label 'Nice.try' in main scope
+ERROR: sym-scope.asm(17):
+    Not currently in the scope of 'Parentheses.check'
+ERROR: sym-scope.asm(21):
+    Not currently in the scope of 'Parent.check'
+error: Assembly aborted (4 errors)!