[irgen] Make HasAArch64TBI an IRGen option instead of a LangOpts.

With some changes that I am making, we will no longer need this flag at the SIL
level, so we can just make it an IRGen flag (which it really should have been
in the first place).

lib/DriverTool/sil_llvm_gen_main.cpp

@@ -167,6 +167,7 @@ int sil_llvm_gen_main(ArrayRef<const char *> argv, void *MainAddr) {
   IRGenOptions &Opts = Invocation.getIRGenOptions();
   Opts.OutputKind = options.OutputKind;
   Opts.DisableLegacyTypeInfo = options.DisableLegacyTypeInfo;
+  Invocation.computeAArch64TBIOptions();
 
   serialization::ExtendedValidationInfo extendedInfo;
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> FileBufOrErr =