Add portable Windows build and update GC runtime

docs/stage_ext.pat

@@ -0,0 +1,58 @@
+// Groove Coaster Android/arcade *_ext.dat
+// LoadExtData starts reading at byte 6. Bytes after notes are not consumed by
+// the recovered Android routine and are intentionally left untyped.
+
+struct NoteTimingEntry {
+    u32 timeMs;
+    u32 mode;
+    float value;
+} [[single_color]];
+struct NoteTimingList {
+    u16 size;
+    NoteTimingEntry entries[size];
+} [[single_color]];
+
+enum NoteType : u8 {
+    NONE = 0,
+    NORMAL = 1,
+    FLICK = 2,
+    HOLD = 3,
+    SCRATCH = 4,
+    BEAT = 5,
+    MERRY_GO_ROUND = 6,
+    HIDDEN = 7,
+    HIDDEN2 = 8,
+    CRITICAL = 9,
+    SLIDE_HOLD = 10,
+    SLIDE_COUNTER = 11,
+    TURN = 12,
+    SPIN = 13,
+    FINISH = 14,
+    DUAL_HOLD = 15,
+};
+struct Note {
+    u32 timeMs;
+    NoteType type;
+    u8 typeOverride;
+    s16 params16[9];
+    u8 flag24;
+    float params25[3];
+    u8 flag37;
+    u8 flag38;
+    float params39[4];
+    u32 params55[3];
+    float param67;
+    u32 param71;
+    float params75[5];
+    u32 param95;
+} [[single_color]];
+
+struct StageExtension {
+    NoteTimingList noteTimings[4];
+    u32 unknown;
+    u32 noteCount;
+    Note notes[noteCount];
+};
+
+u8 prefix[6] @ 0x00;
+StageExtension extension @ 0x06;