Add missing new method to clang::serialization::DataStreamBasic{Reader,Writer} subclasses

See llvm/llvm-project#134142

Author: AnthonyLatsis

include/swift/ClangImporter/SwiftAbstractBasicReader.h

@@ -64,6 +64,11 @@ class DataStreamBasicReader
     return uint32_t(asImpl().readUInt64());
   }
 
+  clang::UnsignedOrNone readUnsignedOrNone() {
+    return clang::UnsignedOrNone::fromInternalRepresentation(
+        unsigned(asImpl().readUInt64()));
+  }
+
   clang::Selector readSelector() {
     uint64_t numArgsPlusOne = asImpl().readUInt64();
 

include/swift/ClangImporter/SwiftAbstractBasicWriter.h

@@ -61,6 +61,10 @@ class DataStreamBasicWriter
     asImpl().writeUInt64(uint64_t(value));
   }
 
+  void writeUnsignedOrNone(clang::UnsignedOrNone value) {
+    asImpl().writeUInt64(uint64_t(value.toInternalRepresentation()));
+  }
+
   void writeSelector(clang::Selector selector) {
     if (selector.isNull()) {
       asImpl().writeUInt64(0);