libxcrypt: Fix the build on Android by allowing warnings

This fixes:

```
lib/util-xbzero.c:61:3: error: extension used [-Werror,-Wlanguage-extension-token]
OBSERVE_MEM (s, len);
^
lib/util-xbzero.c:45:3: note: expanded from macro 'OBSERVE_MEM'
asm volatile ("" : : "m" (*(const char (*)[len]) s))
^
```

pkgs/development/libraries/libxcrypt/default.nix

···
     "--enable-hashes=all"
     "--enable-obsolete-api=glibc"
     "--disable-failure-tokens"
-  ] ++ lib.optionals stdenv.hostPlatform.isMusl [
+  ] ++ lib.optionals (stdenv.hostPlatform.isMusl || stdenv.hostPlatform.libc == "bionic") [
     "--disable-werror"
   ];