community: [libpcap] problems with flex and bison dependencies

Package and Environment Details (include every applicable attribute)

• Package Name/Version: libpcap/1.8.1
• Operating System+version: Linux Ubuntu 18.04
• Compiler+version: gcc-7.4
• Conan version: conan 1.15.0
• Python version: Python 3.7.0

Conan profile (output of conan profile show default or conan profile show <profile> if custom profile is in use)

[settings]
os=Linux
os_build=Linux
arch=x86_64
arch_build=x86_64
build_type=Release
compiler=gcc
compiler.version=7
compiler.libcxx=libstdc++11
compiler.libc=glibc
[options]
[build_requires]
[env]

Steps to reproduce (Include if Applicable)

Try to conan install libpcap/1.8.1 without flex and/or bison installed on the system. It looks like the package is supposed to bring in these dependencies itself, but I get build errors in the case that either flex or bison are not system installed (via apt on Ubuntu 18.04 in my case).

Logs (Include/Attach if Applicable)

Without flex:

checking for flex... flex
checking lex output file root... configure: error: cannot find output from flex; giving up
libpcap/1.8.1@bincrafters/stable: 
libpcap/1.8.1@bincrafters/stable: ERROR: Package 'c3004694b293d9c348a7e3a76b9733d3713f5ff5' build failed

With flex (installed via apt) but without bison:

checking for bison... bison -y
checking for capable yacc/bison... insufficient
configure: error: bison -y is insufficient to compile libpcap.
 libpcap requires Bison, Berkeley YACC, or another YACC compatible with them.
libpcap/1.8.1@bincrafters/stable: 
libpcap/1.8.1@bincrafters/stable: ERROR: Package ...