Merge pull request #20877 from apple/revert-20876-revert-20846-swift-5.0-default-to-gold-linker

Re-apply [5.0] Change Default Linker to Gold for AArch64

Author: bob-wilson

lib/Driver/UnixToolChains.cpp

@@ -103,6 +103,7 @@ ToolChain::InvocationInfo toolchains::GenericUnix::constructInvocation(
 std::string toolchains::GenericUnix::getDefaultLinker() const {
   switch (getTriple().getArch()) {
   case llvm::Triple::arm:
+  case llvm::Triple::aarch64:
   case llvm::Triple::armeb:
   case llvm::Triple::thumb:
   case llvm::Triple::thumbeb: