Hybrid: default+installer

[Croydon]

Based on what @SSE4 has done with Bison and what @uilianries with Thrift, I have tried to adopt the same structure for Flex

This is an alternative suggestion for #4 & #5 which is cleaner in my opinion

I could need a little help with getting the installer done. It currently fails with

CDPATH="${ZSH_VERSION+.}:" && cd . && /bin/sh /home/conan/.conan/data/flex_installer/2.6.4/bincrafters/croydon/build/445cf80f611c1d1eda08bde2ebc5066218ca9701/source_subfolder/build-aux/missing aclocal-1.15 -I m4
/home/conan/.conan/data/flex_installer/2.6.4/bincrafters/croydon/build/445cf80f611c1d1eda08bde2ebc5066218ca9701/source_subfolder/build-aux/missing: line 81: aclocal-1.15: command not found
WARNING: 'aclocal-1.15' is missing on your system.
         You should only need it if you modified 'acinclude.m4' or
         'configure.ac' or m4 files included by 'configure.ac'.
         The 'aclocal' program is part of the GNU Automake package:
         <http://www.gnu.org/software/automake>
         It also requires GNU Autoconf, GNU m4 and Perl in order to run:
         <http://www.gnu.org/software/autoconf>
         <http://www.gnu.org/software/m4/>
         <http://www.perl.org/>
make: *** [Makefile:493: aclocal.m4] Error 127

https://travis-ci.com/bincrafters/conan-flex/jobs/196178631#L841

PS: Thanks for playing around with different styles @madebr, since this is a new structure it is important to experiment a little and not settle for the very first idea

[uilianries]

I've started the same idea here: https://github.com/uilianries/conan-flex-bincrafters/tree/testing/2.6.4

But I think we could use your PR instead.

[SSE4]

I agree we can merge for now
I have two local patches to fix CI, hopefully will have them landed tomorrow, one is simply to include MinGW patches only for Windows, second one is to resolve hang in stage1flex

[madebr]

Cross builing flex/2.6.4 for arm won't work because the stage1flex (built for arm) cannot run on x86.
The stage1flex binary needs to be built for the native architecture.

Add the following lines to .travis.yml to test my hypothesis:

      - <<: *linux
        env: CONAN_GCC_VERSIONS=8 CONAN_DOCKER_IMAGE=conanio/gcc8-armv8

[SSE4]

@madebr thanks for the note, I'll check this use-case tomorrow

[Croydon]

Awesome work! 🎉