I haven't ported the spine-libgdx binary format to all the runtimes yet because there are still a few features that might change the format (eg, bounding boxes). Until then, you could port it yourself. You can implement readFloat something like this:
unsigned char b1 = fgetc(_file);
unsigned char b2 = fgetc(_file);
unsigned char b3 = fgetc(_file);
unsigned char b4 = fgetc(_file);
union {
int i;
float f;
} intToFloat;
intToFloat.i = (long)((b1 << 24) + (b2 << 16) + (b3 << 8) + (b4 << 0));
float value = (float)intToFloat.f;