Use builtin BC decompression when libsquish not available
Use builtin BC decompression when libsquish not available

Builtin code is revived and fixed.

pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1,pixelpicosean/my-godot-2.1