Move yaml::Stream's dtor out of line so it can see Scanner's dtor.

llvm-svn: 154004
diff --git a/llvm/lib/Support/YAMLParser.cpp b/llvm/lib/Support/YAMLParser.cpp
index 475c2e5..330519f 100644
--- a/llvm/lib/Support/YAMLParser.cpp
+++ b/llvm/lib/Support/YAMLParser.cpp
@@ -1523,6 +1523,8 @@
   : scanner(new Scanner(Input, SM))
   , CurrentDoc(0) {}
 
+Stream::~Stream() {}
+
 bool Stream::failed() { return scanner->failed(); }
 
 void Stream::printError(Node *N, const Twine &Msg) {