[ORC] Add an early out for MachOPlatform's init-scraper plugin setup.

If there's no initializer symbol in the current MaterializationResponsibility
then bail out without installing JITLink passes: they're going to be no-ops
anyway.

llvm/lib/ExecutionEngine/Orc/MachOPlatform.cpp

@@ -299,6 +299,9 @@ void MachOPlatform::InitScraperPlugin::modifyPassConfig(
     MaterializationResponsibility &MR, const Triple &TT,
     jitlink::PassConfiguration &Config) {
 
+  if (!MR.getInitializerSymbol())
+    return;
+
   Config.PrePrunePasses.push_back([this, &MR](jitlink::LinkGraph &G) -> Error {
     JITLinkSymbolVector InitSectionSymbols;
     preserveInitSectionIfPresent(InitSectionSymbols, G, "__mod_init_func");