[IRGen] Don't use GOTPCREL relocations for x86 ELF.

Unforunately, x86 ELF linkers like to optimize GOTPCREL relocations by
replacing `mov` instructions that go via the GOT with `lea` instructions
that do not.

That would be fine, but they aren't very selective and will happily
perform this transformation in non-code sections if they think that
the bytes before a relocation look like a `mov` instruction.

This corrupts our metadata.

rdar://148168098

Author: al45tair

lib/IRGen/GenDecl.cpp

@@ -3699,13 +3699,15 @@ static llvm::GlobalVariable *createGOTEquivalent(IRGenModule &IGM,
                                       llvm::GlobalValue::PrivateLinkage,
                                       global,
                                       llvm::Twine("got.") + globalName);
-  
+
   // rdar://problem/53836960: i386 ld64 also mis-links relative references
   // to GOT entries.
   // rdar://problem/59782487: issue with on-device JITd expressions.
   // The JIT gets confused by private vars accessed across object files.
+  // rdar://148168098: ELF x86 GOTPCREL relaxation can break metadata.
   if (!IGM.getOptions().UseJIT &&
-      (!IGM.Triple.isOSDarwin() || IGM.Triple.getArch() != llvm::Triple::x86)) {
+      (!IGM.Triple.isOSDarwin() || IGM.Triple.getArch() != llvm::Triple::x86) &&
+      (!IGM.Triple.isOSBinFormatELF() || !IGM.Triple.isX86())) {
     gotEquivalent->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
   } else {
     ApplyIRLinkage(IRLinkage::InternalLinkOnceODR)