[NCGenerics] disable mangling roundtrip checking

This is a temporary measure until I get a chance to fix the symbol
mangling. This round-tripper is exactly flagging the current
known issue in that all of the symbols get extra `Copyable` and
`Escapable` requirements mangled into them, and thus reconsituting the
type from the mangled name doesn't give you the same type back.

Author: kavon

stdlib/cmake/modules/SwiftSource.cmake

@@ -613,6 +613,7 @@ function(_compile_swift_files
 
   if(SWIFT_STDLIB_EXPERIMENTAL_NONCOPYABLE_GENERICS)
     list(APPEND swift_flags "-enable-experimental-feature" "NoncopyableGenerics")
+    list(APPEND swift_flags "-Xfrontend" "-disable-round-trip-debug-types") # NOTE: temporary until we fix mangling!
   endif()
 
   if (SWIFT_STDLIB_USE_RELATIVE_PROTOCOL_WITNESS_TABLES)