[cxx-interop] Migrate to overlay the new compiler flag

`-enable-experimental-cxx-interop` is deprecated, the new flag for enabling C++ interop is `-cxx-interoperability-mode=enabled`.

NFC intended.

Author: egorzhdan

stdlib/public/Cxx/CMakeLists.txt

@@ -19,7 +19,7 @@ add_swift_target_library(swiftCxx STATIC NO_LINK_NAME IS_STDLIB IS_SWIFT_ONLY IS
     UnsafeCxxIterators.swift
 
     SWIFT_COMPILE_FLAGS ${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS} ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
-    -Xfrontend -enable-experimental-cxx-interop
+    -cxx-interoperability-mode=default
     # This module should not pull in the C++ standard library, so we disable it explicitly.
     # For functionality that depends on the C++ stdlib, use C++ stdlib overlay (`swiftstd` module).
     -Xcc -nostdinc++

stdlib/public/Cxx/std/CMakeLists.txt

@@ -45,7 +45,7 @@ add_swift_target_library(swiftCxxStdlib STATIC NO_LINK_NAME IS_STDLIB IS_SWIFT_O
     SWIFT_MODULE_DEPENDS_MACCATALYST ${swift_cxxstdlib_darwin_dependencies}
 
     SWIFT_COMPILE_FLAGS ${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS} ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
-    -Xfrontend -enable-experimental-cxx-interop
+    -cxx-interoperability-mode=default
     -Xfrontend -module-interface-preserve-types-as-written
 
     SWIFT_COMPILE_FLAGS_LINUX