Tentative fix for semantic3 on imported modules and unnecessary template

function definition issue. Please test!
Also change linkage of __interfaceInfos to external (same as __Class, __vtbl,
__init). The other change might make this superfluous.

gen/llvmhelpers.cpp

@@ -1371,6 +1371,11 @@ bool mustDefineSymbol(Dsymbol* s)
     {
         if (fd->isArrayOp)
             return true;
+            
+        // we can't (and probably shouldn't?) define functions 
+        // that weren't semantic3'ed
+        if (fd->semanticRun < 4)
+            return false;
     }
 
     TemplateInstance* tinst = DtoIsTemplateInstance(s);