[ModuleInterface] Test that ModuleInterfaceExportAs doesn't raise errors

Passing the flags `-enable-experimental-feature ModuleInterfaceExportAs`
has no effect anymore, test that it's not reported as an error.

Author: xymus

test/ModuleInterface/export-as-in-swiftinterfaces.swift

@@ -10,8 +10,7 @@
 // RUN:   -enable-library-evolution \
 // RUN:   -emit-module-path %t/Exported.swiftmodule \
 // RUN:   -emit-module-interface-path %t/Exported.swiftinterface \
-// RUN:   -emit-private-module-interface-path %t/Exported.private.swiftinterface \
-// RUN:   -enable-experimental-feature ModuleInterfaceExportAs
+// RUN:   -emit-private-module-interface-path %t/Exported.private.swiftinterface
 // RUN: %target-swift-typecheck-module-from-interface(%t/Exported.private.swiftinterface) -module-name Exported -I %t
 // RUN: cat %t/Exported.swiftinterface | %FileCheck -check-prefix=CHECK-USE-EXPORTER %s
 // RUN: cat %t/Exported.private.swiftinterface | %FileCheck -check-prefix=CHECK-USE-EXPORTED %s

test/ModuleInterface/swift-export-as.swift

@@ -1,6 +1,10 @@
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
 
+/// Make sure the flag `ModuleInterfaceExportAs` doesn't raise an error.
+// RUN: %target-swift-frontend -emit-module %t/PrivateLib.swift \
+// RUN:   -enable-experimental-feature ModuleInterfaceExportAs
+
 /// Build exportee.
 // RUN: %target-swift-frontend -emit-module %t/PrivateLib.swift \
 // RUN:   -swift-version 5 -enable-library-evolution \