This commit overhauls the libMesh package script in a number of ways:
* We now inherit from AutotoolsPackage.
* libMesh contains about a dozen third-party dependencies that can
only be provided by the copy bundled with libMesh. This patch
enumerates all such bundled dependencies and disables all of them
by default.
* libMesh supports compilation with external installations of boost,
eigen, hdf5, slepc, and tbb; this patch adds all of them to
package.py.
* libMesh will look for a few system executables (xz, bzip, gdb) by
default. This is now disabled.
* libMesh will now used a copy of perl installed by spack instead of
trying to find the system copy.
* Compilation with non-system MPI installations requires an additional
flag (--with-mpi=); this has been added.
- remove the old LGPL license headers from all files in Spack
- add SPDX headers to all files
- core and most packages are (Apache-2.0 OR MIT)
- a very small number of remaining packages are LGPL-2.1-only
