[Orc] Teach IndirectStubsManager to manage an expandable pool of stubs, rather
than a pre-allocated slab of stubs. Also add a convenience method for creating a
single stub, rather than a whole block a time.

llvm-svn: 251658
diff --git a/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp b/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp
index bfed9bb..ecfefe4 100644
--- a/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp
+++ b/llvm/unittests/ExecutionEngine/Orc/CompileOnDemandLayerTest.cpp
@@ -33,6 +33,11 @@
 
 class DummyStubsManager : public orc::IndirectStubsManagerBase {
 public:
+  std::error_code createStub(StringRef StubName, TargetAddress InitAddr,
+                             JITSymbolFlags Flags) override {
+    llvm_unreachable("Not implemented");
+  }
+
   std::error_code createStubs(const StubInitsMap &StubInits) override {
     llvm_unreachable("Not implemented");
   }