Diablo and Hellfire have different palettes in `ui_art\black.pcx`.
We now ship our own tiny `black.pcx` that takes priority over the
other ones. This `black.pcx` had the Diablo palette which resulted in an
incorrect palette in the Settings screen.
Split our own `black.pcx` file into `black_diablo.pcx` and
`black_hellfire.pcx` and load the correct one depending on the mode.
1. Make the vcpkg hack minimal by only defining the options it needs
before `include(Platforms)`.
Every dependent option needed by vcpkg has to be recalculated
after `include(Platforms)`. This brings the count of such options
down to 1 (`PACKET_ENCRYPTION`).
2. `include(Platforms)` before the rest of the options.
3. Group related options together into sections and add comments.
4. Fix `--gc-sections` for C files. Also adds `-Wl,--as-needed`.
Note: `PIE` can now be `ON` even if `BUILD_TESTING` is `OFF`.
