GL_S3_s3tc
https://www.khronos.org/registry/OpenGL/extensions/S3/S3_s3tc.txt
GL_RGB_S3TC 0x83A0
GL_RGB4_S3TC 0x83A1
GL_RGBA_S3TC 0x83A2
GL_RGBA4_S3TC 0x83A3
GL_RGBA_DXT5_S3TC 0x83A4
GL_RGBA4_DXT5_S3TC 0x83A5