Compile error with ppp package on master branch

For Developers
1 
make V=s
--- cut -- begin
arm-buildroot-linux-gnueabi-gcc -Os -pipe -fno-caller-saves -mfloat-abi=soft  -ffunction-sections -fdata-sections -DHAVE_PATHS_H -DHAVE_MMAP -I../include '-DDESTDIR="/usr"' -DCHAPMS=1 -DMPPE=1 -DHAS_SHADOW -DHAVE_CRYPT_H=1 -DHAVE_LOGWTMP=1 -DUSE_CRYPT=1 -DPLUGIN -DPPP_FILTER -DPPP_PRECOMPILED_FILTER -I/home/gqin/LEDE/openwrt/staging_dir/target-arm-buildroot-linux-gnueabi_glibc/usr/include -DINET6=1 -DMAXOCTETS   -c -o pppcrypt.o pppcrypt.c

pppcrypt.c: In function 'DesSetkey':
pppcrypt.c:122:2: warning: implicit declaration of function 'setkey'; did you mean 'DesSetkey'? [-Wimplicit-function-declaration]
  setkey((const char *)crypt_key);
  ^~~~~~
  DesSetkey
pppcrypt.c: In function 'DesEncrypt':
pppcrypt.c:137:2: warning: implicit declaration of function 'encrypt'; did you mean 'crypt'? [-Wimplicit-function-declaration]
  encrypt((char *)des_input, 0);
  ^~~~~~~
  crypt
...
bin/ld: pppcrypt.o: in function `DesSetkey':
pppcrypt.c:(.text.DesSetkey+0xa8): undefined reference to `setkey'
/ld: pppcrypt.o: in function `DesEncrypt':
pppcrypt.c:(.text.DesEncrypt+0x2c): undefined reference to `encrypt'
ld: pppcrypt.o: in function `DesDecrypt':
pppcrypt.c:(.text.DesDecrypt+0x2c): undefined reference to `encrypt'
collect2: error: ld returned 1 exit status
Makefile:238: recipe for target 'pppd' failed
make[4]: *** [pppd] Error 1
--- cut end

latest master branch using external toolchain. any comments? thanks a lot

thanks,
Qin Guang