[JITLink] Add a shouldAddDefaultPasses predicate to JITLinkerBase.

This allows JITLinkerBase implementations to check whether default passes
should be added. The ELF_x86_64 backend is updated to check this predicate
before installing the getOrCreateGOTSymbol pass.

This is an alternative solution to https://reviews.llvm.org/D158909.

llvm/lib/ExecutionEngine/JITLink/ELF_x86_64.cpp

@@ -242,8 +242,10 @@ public:
                       std::unique_ptr<LinkGraph> G,
                       PassConfiguration PassConfig)
       : JITLinker(std::move(Ctx), std::move(G), std::move(PassConfig)) {
-    getPassConfig().PostAllocationPasses.push_back(
-        [this](LinkGraph &G) { return getOrCreateGOTSymbol(G); });
+
+    if (shouldAddDefaultTargetPasses(G->getTargetTriple()))
+      getPassConfig().PostAllocationPasses.push_back(
+          [this](LinkGraph &G) { return getOrCreateGOTSymbol(G); });
   }
 
 private:

llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.h

@@ -43,6 +43,13 @@ protected:
   using AllocResult = Expected<std::unique_ptr<InFlightAlloc>>;
   using FinalizeResult = Expected<JITLinkMemoryManager::FinalizedAlloc>;
 
+  // Returns true if the context says that the linker should add default
+  // passes. This can be used by JITLinkerBase implementations when deciding
+  // whether they should add default passes.
+  bool shouldAddDefaultTargetPasses(const Triple &TT) {
+    return Ctx->shouldAddDefaultTargetPasses(TT);
+  }
+
   // Returns the PassConfiguration for this instance. This can be used by
   // JITLinkerBase implementations to add late passes that reference their
   // own data structures (e.g. for ELF implementations to locate / construct