[TBD] Don't add main entrypoint for statically linked libs

Only add the main symbol for the current module
we're emitting TBD for. This is to avoid hitting
a duplicate symbol assertion when we start always
passing a StringSet to TBDGenVisitor.

Author: hamishknight

lib/TBDGen/TBDGenVisitor.h

@@ -113,7 +113,10 @@ class TBDGenVisitor : public ASTVisitor<TBDGenVisitor> {
     // HACK: 'main' is a special symbol that's always emitted in SILGen if
     //       the file has an entry point. Since it doesn't show up in the
     //       module until SILGen, we need to explicitly add it here.
-    if (file->hasEntryPoint())
+    //
+    // Make sure to only add the main symbol for the module that we're emitting
+    // TBD for, and not for any statically linked libraries.
+    if (file->hasEntryPoint() && file->getParentModule() == SwiftModule)
       addSymbol("main");
   }