* libunwind: add version 1.3-rc1 and variant xz
Version 1.3-rc1 is the latest published snapshot from libunwind.
Variant xz adds spack-built support for reading compressed symbol
tables, or else disables this feature. Without the variant, libunwind
will look for liblzma in /usr/lib.
* Add preferred=True to version 1.2.1 as the last official stable
release.
This commit begins addressing the ideas discussed in #8823. The
libunwind library now provides the "unwind" virtual package, which
represents the "libunwind base API" common to LLVM libunwind, Apple's
LLVM libunwind, and non-GNU libunwind.
Package repositories now look like this:
top-level-dir/
repo.yaml
packages/
libelf/
package.py
mpich/
package.py
...
This leaves room at the top level for additional metadata, source,
per-repo configs, indexes, etc., and it makes it easy to see that
something is a spack repo (just look for repo.yaml and packages).
