[ORC] Rename MultiThreadedSimpleCompiler to ConcurrentIRCompiler.

The new name is a better fit: This class does not actually spawn any new
threads for compilation, it is just safe to call from multiple threads
concurrently.

The "Simple" part of the name did not convey much either, so it was
dropped.

llvm-svn: 344567
diff --git a/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp b/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
index 39bb4c4..478ac2e 100644
--- a/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
@@ -96,7 +96,7 @@
       ObjLinkingLayer(*this->ES,
                       [this](VModuleKey K) { return getMemoryManager(K); }),
       CompileLayer(*this->ES, ObjLinkingLayer,
-                   MultiThreadedSimpleCompiler(std::move(JTMB))),
+                   ConcurrentIRCompiler(std::move(JTMB))),
       CtorRunner(Main), DtorRunner(Main) {
   assert(NumCompileThreads != 0 &&
          "Multithreaded LLJIT instance can not be created with 0 threads");