Fixes handling logic for i386/ELF GOTPC relocation

[jain98]

Summary

The i386/ELF JITLink backend was not correctly handling the GOTPC relocation
by skipping the in-built addend, which was manifesting itself in the form of
a segmentation fault in the LF_external_to_absolute_conversion.s test. This
CR has fixed that issue.

[lhames]

LGTM. Thanks @jain98!

llvm/lib/ExecutionEngine/JITLink/ELF_i386.cpp

 //===----- ELF_i386.cpp - JIT linker implementation for ELF/i386 ----===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // ELF/i386 jit-link implementation.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ExecutionEngine/JITLink/ELF_i386.h"
+#include "DefineExternalSectionStartAndEndSymbols.h"
 #include "ELFLinkGraphBuilder.h"
 #include "JITLinkGeneric.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/ExecutionEngine/JITLink/i386.h"
 #include "llvm/Object/ELFObjectFile.h"
 
-#include "DefineExternalSectionStartAndEndSymbols.h"
-
 #define DEBUG_TYPE "jitlink"
 
 using namespace llvm;
 using namespace llvm::jitlink;
 
 namespace {
 constexpr StringRef ELFGOTSymbolName = "_GLOBAL_OFFSET_TABLE_";
 
if (!GraphSymbol)
                   SymbolIndex, (*ObjSymbol)->st_shndx,
                   Base::GraphSymbols.size()),
           inconvertibleErrorCode());
 
     Expected<i386::EdgeKind_i386> Kind = getRelocationKind(Rel.getType(false));
     if (!Kind)
       return Kind.takeError();
 
+    auto FixupAddress = orc::ExecutorAddr(FixupSection.sh_addr) + Rel.r_offset;
     int64_t Addend = 0;
 
-    auto FixupAddress = orc::ExecutorAddr(FixupSection.sh_addr) + Rel.r_offset;
+    switch (*Kind) {
+    case i386::EdgeKind_i386::Delta32: {
+      const char *FixupContent = BlockToFix.getContent().data() +
+                                 (FixupAddress - BlockToFix.getAddress());
+      Addend = *(const support::ulittle32_t *)FixupContent;
+      break;
+    }
+    }
+
     Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress();
     Edge GE(*Kind, Offset, *GraphSymbol, Addend);
     LLVM_DEBUG({
       dbgs() << "    ";
       printEdge(dbgs(), BlockToFix, GE, i386::getEdgeKindName(*Kind));
       dbgs() << "\n";
     });