error on complile ocserv 0.11.X

[EdmondChu at focuswinhk.com]

I am OK to compile 0.10.x but 0.11.x
with following error

configure: WARNING:
***
*** autogen not found. Will not link against libopts.
***
checking for sighandler_t... yes
checking for sig_t... yes
checking for __sighandler_t... yes
checking for struct ucred... yes
checking for struct iphdr.ihl... yes
checking size of unsigned long... 8
checking whether byte ordering is bigendian... no
checking for LIBNETTLE... no
configure: error: Package requirements (nettle >= 2.7) were not met:

No package 'nettle' found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables LIBNETTLE_CFLAGS
and LIBNETTLE_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.

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