[ORC] Add an 'intern' method to ExecutionEngine for interning symbol names.

This cuts down on boilerplate by reducing 'ES.getSymbolStringPool().intern(...)'
to 'ES.intern(...)'.

llvm-svn: 343427
diff --git a/llvm/lib/ExecutionEngine/Orc/Layer.cpp b/llvm/lib/ExecutionEngine/Orc/Layer.cpp
index f74f1c8..323e1d2 100644
--- a/llvm/lib/ExecutionEngine/Orc/Layer.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/Layer.cpp
@@ -170,7 +170,7 @@
     auto Name = Sym.getName();
     if (!Name)
       return Name.takeError();
-    auto InternedName = ES.getSymbolStringPool().intern(*Name);
+    auto InternedName = ES.intern(*Name);
     auto SymFlags = JITSymbolFlags::fromObjectSymbol(Sym);
     if (!SymFlags)
       return SymFlags.takeError();