Move JIT listener C binding definitions to ExecutionEngineBindings.cpp.

[anarazel]

Summary

Initially, in https://reviews.llvm.org/D44890, I had these defined as
empty functions when the respective event listener was not built
in. As done in that commit, that wasn't correct, because it was a ODR
violation. Krasimir hot-fixed that in r333265, but that wasn't quite
right either, because it'd lead to the symbol not being available.

Instead just move the function definition unconditionally to
ExecutionEngineBindings.cpp. That solves both problems. No ifdefs
needed, the ones in JITEventListener are sufficient.

[anarazel]

Previous approach was a brick shy of a load, which I realized after
sleeping on it. We'd just end up with undefined symbol errors for the
listeners that *are* built in (because the part of the class
implementation ptentially is in a different lib). Hence just define
if necessary.

llvm/trunk/include/llvm/ExecutionEngine/JITEventListener.h

 private:
   virtual void anchor();
 };
 
 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(JITEventListener, LLVMJITEventListenerRef)
 
 } // end namespace llvm
 
-#ifndef LLVM_USE_INTEL_JITEVENTS
-LLVMJITEventListenerRef LLVMCreateIntelJITEventListener(void);
-#endif
-
-#ifndef LLVM_USE_OPROFILE
-LLVMJITEventListenerRef LLVMCreateOProfileJITEventListener(void);
-#endif
-
-#ifndef LLVM_USE_PERF
-LLVMJITEventListenerRef LLVMCreatePerfJITEventListener(void);
-#endif
-
 #endif // LLVM_EXECUTIONENGINE_JITEVENTLISTENER_H

llvm/trunk/lib/ExecutionEngine/ExecutionEngineBindings.cpp

 //===-- ExecutionEngineBindings.cpp - C bindings for EEs ------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the C bindings for the ExecutionEngine library.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm-c/ExecutionEngine.h"
 #include "llvm/ExecutionEngine/ExecutionEngine.h"
 #include "llvm/ExecutionEngine/GenericValue.h"
+#include "llvm/ExecutionEngine/JITEventListener.h"
 #include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Target/CodeGenCWrappers.h"
 #include "llvm/Target/TargetOptions.h"
 #include <cstring>
 
LLVMMCJITMemoryManagerRef LLVMCreateSimpleMCJITMemoryManager(
   functions.Destroy = Destroy;
   return wrap(new SimpleBindingMemoryManager(functions, Opaque));
 }
 
 void LLVMDisposeMCJITMemoryManager(LLVMMCJITMemoryManagerRef MM) {
   delete unwrap(MM);
 }
 
+/*===-- JIT Event Listener functions -------------------------------------===*/
+
+
+#if !LLVM_USE_INTEL_JITEVENTS
+LLVMJITEventListenerRef LLVMCreateIntelJITEventListener(void)
+{
+  return nullptr;
+}
+#endif
+
+#if !LLVM_USE_OPROFILE
+LLVMJITEventListenerRef LLVMCreateOProfileJITEventListener(void)
+{
+  return nullptr;
+}
+#endif
+
+#if !LLVM_USE_PERF
+LLVMJITEventListenerRef LLVMCreatePerfJITEventListener(void)
+{
+  return nullptr;
+}
+#endif