Build with gpu parallelization fails

```
$> codon build -release mandelbrot_gpu.codon
/usr/bin/ld: mandelbrot_gpu.o: in function `main':
mandelbrot_gpu.codon:(.text+0x2ae): undefined reference to `seq_nvptx_load_module'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x3cb): undefined reference to `seq_nvptx_device_alloc'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x3dc): undefined reference to `seq_nvptx_memcpy_h2d'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x3f8): undefined reference to `seq_nvptx_device_alloc'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x410): undefined reference to `seq_nvptx_memcpy_h2d'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x45f): undefined reference to `seq_nvptx_function'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x4a4): undefined reference to `seq_nvptx_invoke'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x4ca): undefined reference to `seq_nvptx_memcpy_d2h'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x510): undefined reference to `seq_nvptx_memcpy_d2h'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x51b): undefined reference to `seq_nvptx_device_free'
/usr/bin/ld: mandelbrot_gpu.codon:(.text+0x523): undefined reference to `seq_nvptx_device_free'
```

gpu: GTX 1050ti