[ORC] Rename NullResolver to NullLegacyResolver.

This resolver conforms to the LegacyJITSymbolResolver interface, and will be
replaced with a null-returning resolver conforming to the newer
orc::SymbolResolver interface in the near future. This patch renames the class
to avoid a clash.

llvm-svn: 324175
diff --git a/llvm/lib/ExecutionEngine/Orc/NullResolver.cpp b/llvm/lib/ExecutionEngine/Orc/NullResolver.cpp
index 8f2d6fd..6bb94f7 100644
--- a/llvm/lib/ExecutionEngine/Orc/NullResolver.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/NullResolver.cpp
@@ -14,11 +14,12 @@
 namespace llvm {
 namespace orc {
 
-JITSymbol NullResolver::findSymbol(const std::string &Name) {
+JITSymbol NullLegacyResolver::findSymbol(const std::string &Name) {
   llvm_unreachable("Unexpected cross-object symbol reference");
 }
 
-JITSymbol NullResolver::findSymbolInLogicalDylib(const std::string &Name) {
+JITSymbol
+NullLegacyResolver::findSymbolInLogicalDylib(const std::string &Name) {
   llvm_unreachable("Unexpected cross-object symbol reference");
 }