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/enums.h	Sun Jun 07 15:07:29 2009 +0200
+++ b/gen/enums.h	Sun Jun 07 16:00:13 2009 +0200
@@ -9,6 +9,5 @@
     LLVMva_copy,
     LLVMva_end,
     LLVMva_arg,
-    LLVMldc,
     LLVMinline_asm
 };