for some reason bison 3.7 output references $x_defs.h files under the name
$x.hpp. create symlinks to make this work.

(cherry picked from commit 53a8a41)

it may be possible to get it building under clang with some work, but
switching it to gcc for now allows us to enable it

(cherry picked from commit fc709e6)

[20.09] cvc3: fix build against bison 3.7

There are a variety of additional scripts that are included with the
JRuby installation that use JRuby itself.

For instance the `bin/gem` had the following contents:

```bash
❯ cat /nix/store/kglkqf56ii83yl6yrgcaj5r3s9m2fzr0-jruby-9.2.13.0/bin/gem

load File.join(File.dirname(__FILE__), 'jgem')
```

This is clearly wrong. Patchshebangs was not picking up the fix as part
of stdenv because the patch is not a build input but the final output
itself.

We have to rely on substituteInPlace so that we get the correct version.

```bash
❯ cat /nix/store/k4fnrn0dcsh2wzw81217r0ywsspb468f-jruby-9.2.13.0/bin/gem

```

(cherry picked from commit 8da7bd6)

(cherry picked from commit 0a07c8c)

(cherry picked from commit f5c2f51)

(cherry picked from commit 6b0794c)