Run `semantic3` on imported modules, and emit new symbols with `available_externally` linkage. This allows the inliner to inline functions from other modules while telling the code generator to ignore those functions (treat them as declarations) Still generates a few extra `TypeInfo`s and strings... Disabled when generating debug info because I don't really understand it, and it doesn't like this.

--- a/gen/classes.cpp	Sun Jun 07 15:07:29 2009 +0200
+++ b/gen/classes.cpp	Sun Jun 07 16:00:13 2009 +0200
@@ -491,7 +491,9 @@
     {
         Logger::cout() << "src2: " << *src << '\n';
         Logger::cout() << "index: " << field->index << '\n';
+#if 0
         Logger::cout() << "srctype: " << *src->getType() << '\n';
+#endif
     }
 #endif
     LLValue* val = DtoGEPi(src, 0, field->index);