Use the g++ `-fabi-version=2` compiler option, as suggested by @ArtiiP
to fix problems similar to:

```
Fatal Error: Mismatch between the program and library build versions
detected.
The library used 3.0 (wchar_t,compiler with C++ ABI 1002,wx
containers,compatible with 2.8),
and your program used 3.0 (wchar_t,compiler with C++ ABI 1009,wx
containers,compatible with 2.8).
Aborted
```

Turn LTO off by default until I fix it for newer gcc/binutils, currently
with gcc7 ar segfaults linking vbamcore.