[IRGen] Corrected size of trailing flags field.

The struct and enum metadata scanners were both adding a pointer for the
trailing flags field.  That was only correct for 64-bit platforms.
Instead, add an Int64.

Author: nate-chandler

lib/IRGen/ConstantBuilder.h

@@ -77,6 +77,8 @@ class ConstantAggregateBuilderBase
     addInt(IGM().Int32Ty, value);
   }
 
+  void addInt64(uint64_t value) { addInt(IGM().Int64Ty, value); }
+
   void addRelativeAddressOrNull(llvm::Constant *target) {
     if (target) {
       addRelativeAddress(target);

lib/IRGen/EnumMetadataVisitor.h

@@ -94,12 +94,13 @@ class EnumMetadataScanner : public EnumMetadataVisitor<Impl> {
   void addGenericWitnessTable(GenericRequirement requirement) { addPointer(); }
   void addPayloadSize() { addPointer(); }
   void noteStartOfTypeSpecificMembers() {}
-  void addTrailingFlags() { addPointer(); }
+  void addTrailingFlags() { addInt64(); }
 
 private:
   void addPointer() {
     NextOffset += super::IGM.getPointerSize();
   }
+  void addInt64() { NextOffset += Size(8); }
 };
 
 } // end namespace irgen

lib/IRGen/StructMetadataVisitor.h

@@ -104,13 +104,14 @@ class StructMetadataScanner : public StructMetadataVisitor<Impl> {
     NextOffset = NextOffset.roundUpToAlignment(super::IGM.getPointerAlignment());
   }
 
-  void addTrailingFlags() { addPointer(); }
+  void addTrailingFlags() { addInt64(); }
 
 private:
   void addPointer() {
     NextOffset += super::IGM.getPointerSize();
   }
   void addInt32() { NextOffset += Size(4); }
+  void addInt64() { NextOffset += Size(8); }
 };
 
 } // end namespace irgen