update pppd patch and build shell script, fix buildroot glibc build bug

guowenxue

2019-08-11 44b6985a5c9724e5f8b8f30000c5f022dee42863

 3rdparty/dropbear/build.sh

@@ -70,7 +70,7 @@
    SRC_NAME=dropbear-2019.78
    PACK_SUFIX=tar.bz2

    if [ -f ${PREFIX_PATH}/dropbear ] ; then
    if [ -f ${PREFIX_PATH}/bin/dropbear ] ; then
        return 0;
    fi