This was previously manually set to '4.8.0'. Aside from just being incorrect,
it also breaks Errno's GCC5 detection.

Fixes #2044.

Signed-off-by: Marcel Denia <naoir@gmx.net>

This replaces the previously used collection of configuration files for every single
architecture in conjunction with hacky overrides, which became an increasing burden to maintain.

Fixes a number of outstanding bugs and oddities, with the most important one being the
previously wrong signal order(as shown by ext/POSIX/t/sigaction.t).

See files/perlconfig.pl's POD and files/README.config for details.

Signed-off-by: Marcel Denia <naoir@gmx.net>