[pdb] Round trip the PDB stream between YAML and binary PDB.

This gets writing of the PDB stream working.

llvm-svn: 274647
diff --git a/llvm/lib/DebugInfo/PDB/Raw/SymbolStream.cpp b/llvm/lib/DebugInfo/PDB/Raw/SymbolStream.cpp
index c8e93c2..41b2a64 100644
--- a/llvm/lib/DebugInfo/PDB/Raw/SymbolStream.cpp
+++ b/llvm/lib/DebugInfo/PDB/Raw/SymbolStream.cpp
@@ -42,3 +42,5 @@
 SymbolStream::getSymbols(bool *HadError) const {
   return llvm::make_range(SymbolRecords.begin(HadError), SymbolRecords.end());
 }
+
+Error SymbolStream::commit() { return Error::success(); }