bootstrapping 2021.12 compat layer fails on ppc64le due to build problem for libgcrypt

(using commit 1ee7f64 from #126)

```
libs/libgcrypt-1.9.4/work/libgcrypt-1.9.4/cipher/chacha20-ppc.c:60:10: error: argument 3 must be a 4-bit unsigned literal
   60 |   return vec_sld (v, v, (16 - (4 * idx)) & 15);
      |          ^~~~~~~
```

reported upstream at https://bugs.gentoo.org/825722