Merge branch 'config-libdir' into next

Andrea Claudi  says:

====================

This series add support for the libdir parameter in iproute2 configure
script. The idea is to make use of the fact that packaging systems may
assume that 'configure' comes from autotools allowing a syntax similar
to the autotools one, and using it to tell iproute2 where the distro
expects to find its lib files.

Patches 1-2 fix a parsing issue on current configure options, that may
trigger an endless loop when no value is provided with some options;

Patch 3 fixes a parsing issue bailing out when more than one value is
provided for a single option;

Patch 4 simplifies options parsing, moving semantic checks out of the
while loop processing options;

Patch 5 introduces support for the --opt=value style on current options,
for uniformity;

Patch 6 adds the --prefix option, that may be used by some packaging
systems when calling the configure script;

Patch 7 finally adds the --libdir option, and also drops the static
LIBDIR var from the Makefile.

Changelog:
----------
v4 -> v5
  - bail out when multiple values are provided with a single option
  - simplify option parsing and reduce code duplication, as suggested
    by Phil Sutter
  - remove a nasty eval on libdir option processing

v3 -> v4
  - fix parsing issue on '--include_dir' and '--libbpf_dir'
  - split '--opt value' and '--opt=value' use cases, avoid code
    duplication moving semantic checks on value to dedicated functions

v2 -> v3
  - fix parsing error on prefix and libdir options.

v1 -> v2
  - consolidate '--opt value' and '--opt=value' use cases, as suggested
    by David Ahern.
  - added patch 2 to manage the --prefix option, used by the Debian
    packaging system, as reported by Luca Boccassi, and use it when
    setting lib directory.

====================

Signed-off-by: David Ahern <dsahern@kernel.org>