root solver check fails incorrectly for gsl 2.7

See the PR here that appears to have things as solvable: https://github.com/conda-forge/root-feedstock/pull/140

See this error:

```
root (4) Error: not solvable (bot CI job): master: ['linux_64_numpy1.18python3.6.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 2\n', 'linux_64_numpy1.18python3.7.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 2\n', 'linux_64_numpy1.18python3.8.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 2\n', 'linux_64_numpy1.19python3.9.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 2\n', 'linux_aarch64_numpy1.18python3.6.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 3\n', 'linux_aarch64_numpy1.18python3.7.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 3\n', 'linux_aarch64_numpy1.18python3.8.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 3\n', 'linux_aarch64_numpy1.19python3.9.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 3\n', 'linux_ppc64le_numpy1.18python3.6.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 0\n', 'linux_ppc64le_numpy1.18python3.7.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 0\n', 'linux_ppc64le_numpy1.18python3.8.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 0\n', 'linux_ppc64le_numpy1.19python3.9.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 0\n', 'osx_64_numpy1.18python3.6.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 3\n', 'osx_64_numpy1.18python3.7.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 3\n', 'osx_64_numpy1.18python3.8.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 3\n', 'osx_64_numpy1.19python3.9.____cpython: Encountered problems while solving:\n - nothing provides requested libllvm9 9.0.1.* 3\n']
```