ngrep: fix static linking issue with libpcre

Adding -lpcre in LDFLAGS place the library before object files:
gcc ... -lpcre -L.../sysroot/usr/lib -s -o ngrep ngrep.o -lpcap

Makefile.in is patched to use @LIBS@ for adding -lpcre in the right place.

Fixes:
http://autobuild.buildroot.net/results/684/684a3bed28d13ef5e5156257aade3b9aff32f180



[Peter: fixup patch description]
Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>