osx does not come with gcc, actually it is clang. so, remove it.
move debhelper installation to "apt" plugin (it will affect only linux).
add otool (which is ldd equivalent) on osx.
split "before_install", "script" into matrix
* makefiles: add /usr/local/opt/openssl/include and /usr/local/opt/openssl/lib as include paths on MacOS
* Travis CI: add MacOS target and create scripts files