Build fails on Linux: missing <functional> include and unsupported-platform #error

[ajfa]

Two small things stop a Linux build (tested on Ubuntu 22.04, GCC 11.4, Qt 5.15).

1. WindCore/arm710.h misses #include <functional>

The header uses std::function:

void setLogger(std::function<void(const char *)> newLogger) { logger = newLogger; }
...
std::function<void(const char *)> logger;

but only includes <stdint.h>, <optional> and <variant>. With older
libstdc++ this compiled because <optional> pulled <functional> in
transitively; with GCC 11 it does not, and the build fails. Adding the explicit
include fixes it.

2. WindQt/pdascreenwindow.cpp cannot build on non-Windows, non-macOS hosts

#error "Unsupported platform (for now! fix me in pdascreenwindow.cpp)"
static EpocKey resolveKey(int key) {

Besides the #error, the placeholder resolveKey in that branch takes one
argument while both call sites pass two:

EpocKey k = resolveKey(event->key(), event->nativeVirtualKey());

so removing the #error alone is not enough — the fallback also needs the
two-argument signature. With both changed, WindQt builds and runs on
Linux/X11 (we used it under WSLg).

Keyboard mapping on the fallback path is obviously not correct; this is only
about the build.

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Reported by @ajfa, with Claude (Anthropic) assisting.