[ModuleInterface] Remove fallback behavior for arm64e -> arm64.

Addresses rdar://problem/61407215.

Author: varungandhi-apple

lib/Serialization/SerializedModuleLoader.cpp

@@ -49,14 +49,10 @@ void forEachTargetModuleBasename(const ASTContext &Ctx,
   // names checked in "#if arch(...)". Fall back to that name in the one case
   // where it's different from what Swift 4.2 supported:
   // - 32-bit ARM platforms (formerly "arm")
-  // - arm64e (formerly shared with "arm64")
   // We should be able to drop this once there's an Xcode that supports the
   // new names.
-  if (Ctx.LangOpts.Target.getArch() == llvm::Triple::ArchType::arm)
+  if (Ctx.LangOpts.Target.getArch() == llvm::Triple::ArchType::arm) {
     body("arm");
-  else if (Ctx.LangOpts.Target.getSubArch() ==
-           llvm::Triple::SubArchType::AArch64SubArch_E) {
-    body("arm64");
   }
 }
 

test/ModuleInterface/arm64e-fallback.swift

@@ -1,5 +1,6 @@
-// RUN: %target-typecheck-verify-swift %s -target arm64e-apple-ios13.0 -F %S/Inputs
+// RUN: not %target-typecheck-verify-swift -target arm64e-apple-ios13.0 -F %S/Inputs 2>&1 | %FileCheck %s
 
 // REQUIRES: OS=ios
 
 import DummyFramework
+// CHECK: no such module 'DummyFramework'