[Orc] Add conversion to/from RuntimeDyld::SymbolInfo for JITSymbol.

This tidies up some code that was manually constructing RuntimeDyld::SymbolInfo
instances from JITSymbols. It will save more mess in the future when
JITSymbol::getAddress is extended to return an Expected<TargetAddress> rather
than just a TargetAddress, since we'll be able to embed the error checking in
the conversion.

llvm-svn: 271350
diff --git a/llvm/docs/tutorial/BuildingAJIT1.rst b/llvm/docs/tutorial/BuildingAJIT1.rst
index ebaea49..0859100 100644
--- a/llvm/docs/tutorial/BuildingAJIT1.rst
+++ b/llvm/docs/tutorial/BuildingAJIT1.rst
@@ -190,7 +190,7 @@
     auto Resolver = createLambdaResolver(
         [&](const std::string &Name) {
           if (auto Sym = CompileLayer.findSymbol(Name, false))
-            return RuntimeDyld::SymbolInfo(Sym.getAddress(), Sym.getFlags());
+            return Sym.toRuntimeDyldSymbol();
           return RuntimeDyld::SymbolInfo(nullptr);
         },
         [](const std::string &S) {