Support function declarations in the definitions of other functions.

As part of this, function declarations are no longer scoped (this is permitted
by the C standard, as it turns out.)  So code like:

   void foo() { void bar(); }
   void bat() { bar(); }

Compiles correctly; the declaration of bar() in foo() is still available in the
definition of bar().

Fixes issue #129.

decl.h

@@ -210,6 +210,10 @@ public:
         Declarator representation.) */
     std::vector<VariableDeclaration> GetVariableDeclarations() const;
 
+    /** For any function declarations in the Declaration, add the
+        declaration to the module. */
+    void DeclareFunctions();
+
     DeclSpecs *declSpecs;
     std::vector<Declarator *> declarators;
 };