core: link with libarchive on MacOS platform

[dilaroga]

This change allow to link libarchive on mac platform with a default libarchive installation.

[trollixx]

Hi,

Sorry, I won't merge this. I have explained my reasons here.

[apanzerj]

Hey @trollixx just putting a note here for others wondering about this:

You need to change core.pri and add:

macx-clang: {
    INCLUDEPATH += /usr/local/Cellar/libarchive/3.2.1/include
    LIBS += -L/usr/local/Cellar/libarchive/3.2.1/lib -larchive
    INCLUDEPATH += /usr/local/Cellar/sqlite/3.15.0/include
    LIBS += -L/usr/local/Cellar/sqlite/3.15.0/lib -lsqlite3
}

Change the versions to the ones that match your homebrew setup.

I used this document: http://mazhuang.org/2016/01/16/build-zeal-for-mac-osx/

It's in Chinese but google translate does a damn fine job.