Merge remote-tracking branch 'origin/main' into rebranch

lib/Frontend/CompilerInvocation.cpp

@@ -2299,6 +2299,9 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
                      "-num-threads");
     }
   }
+  Opts.UseSingleModuleLLVMEmission =
+      Opts.NumThreads != 0 &&
+      Args.hasArg(OPT_enable_single_module_llvm_emission);
 
   if (SWIFT_ENABLE_GLOBAL_ISEL_ARM64 &&
       Triple.getArch() == llvm::Triple::aarch64 &&