This commit fixes#7900.
In short: in the absence of constraints to the contrary, spack will
download the preferred version of a package, which is usually the most
recent non-develop version. On a clean spack installation without
hypre installed, `spack install mfem` will download hypre 2.14.0,
which is API-incompatible with mfem 3.3.2 (and earlier versions of
mfem), so spack will throw compiler errors re: the API mismatch.
This commit fixes that error by restricting mfem release versions
3.3.2 and earlier to hypre version 2.10.b to 2.13.999 (only 2.13.0
currently exists, but if it has a non-2.14.x maintenance release,
these versions of hypre should also be permitted).
d54ceb6ce7