Revert "Don't generate automatic include guards"

This reverts commit 05e34102d4949a7992f836db13085a85dea7c82c.

Conflicts:
	source/compiler/sc2.c
Introduce compatibility mode

The compiler now has a new command-line option (-Z) that toggles
between normal mode and "compatibility" mode.

When this mode is on the compiler attempts to be compatible with
the current SA-MP compiler, which allows compiling old SA-MP scripts
that would not compile otherwise (because of new breaking changes)
and the same time benefiting from the new features and bug fixes.

In particular, this allows compiling code that relies on the auto
generated #include guard symbols (_inc_filename), though they work differently on Windows and Linux.

And in case you're wondering, the Z in "-Z" does not stand for "Zeex",
it just means "a letter that is unlikely to be ever taken by another
option".

This closes #23.