openwrt外部工具链编译时makedefconfig报错，求助

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在虚拟机ubuntu系统下搭建openwrt环境，在其make之前将另外的交叉编译工具链链接里面
操作如下:
修改[*]Adcanced configurationoptions->
                        [*]Use external toolchain
修改Base system->
                        Libc…configuration->交叉工具链所在路径
                        Libgcc…configuration->交叉工具链所在路径
                        Libpthread…configuration->交叉工具链所在路径
修改后进行make defconfig、及make preqre报错
如下：
cuimh@cuimh-virtual-machine:~/openwrt$ make defconfig
WARNING: Makefile 'package/utils/busybox/Makefile' has a dependency on 'libpam', which does not exist
WARNING: Makefile 'package/utils/busybox/Makefile' has a build dependency on 'libpam', which does not exist
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libgnutls', which does not exist
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libopenldap', which does not exist
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libidn2', which does not exist
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libssh2', which does not exist
WARNING: Makefile 'package/boot/kexec-tools/Makefile' has a dependency on 'liblzma', which does not exist
WARNING: Makefile 'package/network/services/lldpd/Makefile' has a dependency on 'libnetsnmp', which does not exist
#
# configuration written to .config
#
cuimh@cuimh-virtual-machine:~/openwrt$ make prereq
WARNING: Makefile 'package/utils/busybox/Makefile' has a dependency on 'libpam', which does not exist
WARNING: Makefile 'package/utils/busybox/Makefile' has a build dependency on 'libpam', which does not exist
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libgnutls', which does not exist
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libopenldap', which does not exist
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libidn2', which does not exist
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libssh2', which does not exist
WARNING: Makefile 'package/boot/kexec-tools/Makefile' has a dependency on 'liblzma', which does not exist
WARNING: Makefile 'package/network/services/lldpd/Makefile' has a dependency on 'libnetsnmp', which does not exist
time: target/linux/prereq#0.21#0.02#0.28


麻烦大神们帮忙解答一下~~~