This commit updates $license variable in all APKBUILDs to comply with
short names specified by SPDX version 3.0 [1] where possible. It was
done using find-and-replace method on substrings inside $license
variables.

Only license names were updated, not "expressions" specifying relation
between the licenses (e.g. "X and Y", "X or Y", "X and (Y or Z)") or
exceptions (e.g. "X with exceptions").

Many licenses have a version or multiple variants, e.g. MPL-2.0,
BSD-2-Clause, BSD-3-Clause. However, $license in many aports do not
contain license version or variant. Since there's no way how to infer
this information just from abuild, it were left without the variant
suffix or version, i.e. non SPDX compliant.

GNU licenses (AGPL, GFDL, GPL, LGPL) are especially complicated. They
exist in two variants: -only (formerly e.g. GPL-2.0) and -or-later
(formerly e.g. GPL-2.0+). We did not systematically noted distinguish
between these variants, so GPL-2.0, GPL2, GPLv2 etc. may mean
GPL-2.0-only or GPL-2.0-or-later. Thus GNU licenses without "+" (e.g.
GPL2+) were left without the variant suffix, i.e. non SPDX compliant.

Note: This commit just fixes format of the license names, no
verification has been done if the specified license information is
actually correct!

[1]: https://spdx.org/licenses/

* Modernize abuild
* Use elfutils instead of libelf
  - ArchLinux uses elfutils, too
  - Flatpak needs elfutils and libdwarf,
    but libdwarf will install libelf.
    Using elfutils for libdwarf will avoid
    that conflict.

http://libdwarf.sourceforge.net
A library and a set of tools for reading and writing DWARF2 and later debugging information