[JITLink][COFF][x86_64] Stub SECREL relocation to external symbol.

[sunho]

Summary

Stubs SECREL relocation to external symbol. In order to correctly deal with this, we want to requrest memory manager to keep track of address of first block of sepecific section and keep address to be only increased from that point. We also should give jitlink to get information about global section. The relocation is only used for debug and tls info which we don't support yet anyways, so just stubbing it for now.

[lhames]

LGTM.

llvm/lib/ExecutionEngine/JITLink/COFF_x86_64.cpp

case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_SECTION: {
         SectionIdx = COFFSymbol.getSectionNumber();
       auto *AbsSym = &getGraph().addAbsoluteSymbol(
           "secidx", orc::ExecutorAddr(SectionIdx), 2, Linkage::Strong,
           Scope::Local, false);
       GraphSymbol = AbsSym;
       break;
     }
     case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_SECREL: {
+      // FIXME: SECREL to external symbol should be handled
+      if (!GraphSymbol->isDefined())
+        return Error::success();
       Kind = EdgeKind_coff_x86_64::SecRel32;
       Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
       break;
     }
     default: {
       return make_error<JITLinkError>("Unsupported x86_64 relocation:" +
                                       formatv("{0:d}", Rel.getType()));
     }