[gardening] Make sure FieldRecordFlags.Data never contains uninitialized data

This will silence the warning "The left expression of the compound assignment
is an uninitialized value. The computed value will also be garbage."

Author: practicalswift

include/swift/Reflection/Records.h

@@ -32,7 +32,7 @@ class FieldRecordFlags {
     // Is this an indirect enum case?
     IsIndirectCase = 0x1
   };
-  int_type Data;
+  int_type Data = 0;
 
 public:
   bool isIndirectCase() const {