Android: Add io_uring support

Android: Add io_uring support

This patch has been tested on a recent Android phone. Compilation of this
patch has been verified as follows:

    NDK=/usr/lib/android-ndk
    export LIBS="-landroid"
    export UNAME=Android
    for ((i=23;i<=30;i++)); do
        echo "==== i = $i ===="
        export CC=$NDK/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android${i}-clang
        [ -e "$CC" ] || continue
        ./configure && make -j$(nproc) fio || break
    done

Signed-off-by: Bart Van Assche <bvanassche@acm.org>