[libcxx] locale_bionic.h: skip ndk-version.h on Android platform

The Android platform does not have ndk-version.h, but it will always
have up-to-date libc headers, so it does not need any compatibility
code intended for past versions of NDK_MAJOR. If ndk-version.h is missing,
assume NDK_MAJOR is (conceptually) infinite

Bug: https://buganizer.corp.google.com/issues/222341313
Test: None