Fix miscellaneous warnings when building ORCA translator code

- Fix "missing prototype" warnings
- Fix "generalized initializer lists are a C++ extension" warning

funcs.cpp:43:1: warning: no previous prototype for function 'DisableXform' [-Wmissing-prototypes]
DisableXform(PG_FUNCTION_ARGS)
^
funcs.cpp:76:1: warning: no previous prototype for function 'EnableXform' [-Wmissing-prototypes]
EnableXform(PG_FUNCTION_ARGS)
^
funcs.cpp:109:1: warning: no previous prototype for function 'LibraryVersion' [-Wmissing-prototypes]
LibraryVersion()
^
funcs.cpp:123:1: warning: no previous prototype for function 'OptVersion' [-Wmissing-prototypes]
OptVersion()
^
4 warnings generated.

CTranslatorDXLToScalar.cpp:730:9: warning: generalized initializer lists are a C++11 extension [-Wc++11-extensions]
        return { .oid_type = inner_type_oid, .type_modifier = type_modifier};

src/backend/gpopt/translate/CTranslatorDXLToScalar.cpp

@@ -684,7 +684,9 @@ inline CTranslatorDXLToScalar::STypeOidAndTypeModifier OidParamOidFromDXLIdentOr
 	}
 	Oid inner_type_oid = CMDIdGPDB::CastMdid(inner_ident->MdidType())->Oid();
 	INT type_modifier = inner_ident->TypeModifier();
-	return {inner_type_oid, type_modifier};
+
+	CTranslatorDXLToScalar::STypeOidAndTypeModifier modifier = { inner_type_oid, type_modifier};
+	return modifier;
 }
 
 //---------------------------------------------------------------------------

src/backend/gpopt/utils/funcs.cpp

@@ -21,6 +21,7 @@ extern "C" {
 #include "utils/builtins.h"
 }
 
+#include "gpopt/utils/funcs.h"
 #include "gpopt/utils/COptTasks.h"
 
 #include "gpos/_api.h"

src/include/gpopt/CGPOptimizer.h

@@ -44,4 +44,14 @@ class CGPOptimizer
     void TerminateGPOPT();
 };
 
+extern "C"
+{
+
+extern PlannedStmt *GPOPTOptimizedPlan(Query *query, bool *had_unexpected_failure);
+extern char *SerializeDXLPlan(Query *query);
+extern void InitGPOPT ();
+extern void TerminateGPOPT ();
+
+}
+
 #endif // CGPOptimizer_H

src/include/gpopt/utils/funcs.h

+//---------------------------------------------------------------------------
+//
+// funcs.h
+//    API for invoking optimizer using GPDB udfs
+//
+// Copyright (c) 2019-Present Pivotal Software, Inc.
+//
+//---------------------------------------------------------------------------
+
+#ifndef GPOPT_funcs_H
+#define GPOPT_funcs_H
+
+
+extern "C"
+{
+
+#include "postgres.h"
+#include "fmgr.h"
+#include "utils/builtins.h"
+
+extern Datum DisableXform(PG_FUNCTION_ARGS);
+extern Datum EnableXform(PG_FUNCTION_ARGS);
+extern Datum LibraryVersion();
+extern const char * OptVersion(void);
+
+}
+
+#endif // GPOPT_funcs_H