[modules] Mark deleted functions as implicitly inline to allow merging

[EricWF]

Summary

When merging definitions with ModulesLocalVisibility enabled it's important to make deleted definitions implicitly inline, otherwise they'll be diagnosed as a redefinition.

[EricWF]

Add test case.

[rsmith]

lib/Sema/SemaDeclCXX.cpp

13875–13876

This comment is effectively saying "Modules relies on the AST being correct". I don't think we need it.

lib/Sema/SemaDeclCXX.cpp

   if (Fn->isMain())
     Diag(DelLoc, diag::err_deleted_main);
 
+  // C++11 [dcl.fct.def.delete]p4:
+  //  A deleted function is implicitly inline.
+  Fn->setImplicitlyInline();
   Fn->setDeletedAsWritten();
 }
 

test/Modules/Inputs/merge-decl-context/a.h

 struct Aggregate {
   int member;
 };
+bool operator==(Aggregate, Aggregate) = delete;
 
 #endif