[LLJIT] Allow multiple loadPlatformDynamicLibrary calls with the same…

… path.

Where the same dylib is loaded more than once we should just return the
JITDylib created by the first call rather than error out. This matches the
behavior of dlopen / LoadLibrary.

llvm/lib/ExecutionEngine/Orc/LLJIT.cpp

@@ -764,11 +764,8 @@ Expected<JITDylib &> LLJIT::loadPlatformDynamicLibrary(const char *Path) {
   if (!G)
     return G.takeError();
 
-  if (ES->getJITDylibByName(Path))
-    return make_error<StringError>(
-        Twine("LLJIT ExecutionSession already contains a JITDylib named \"") +
-            Path + "\"",
-        inconvertibleErrorCode());
+  if (auto *ExistingJD = ES->getJITDylibByName(Path))
+    return *ExistingJD;
 
   auto &JD = ES->createBareJITDylib(Path);
   JD.addGenerator(std::move(*G));