pkgconf: upgrade 2.0.3 -> 2.1.0

pkgconf: upgrade 2.0.3 -> 2.1.0

Changelog:
===========
* Do not flatten the solver solution into the original world used as
  input to the solver.
* Fix warnings with GCC 14 -Walloc-size.
* Add --solution to the pkgconf CLI to dump the solver state.
* Improve the --digraph output to clarify cancelled edges in a given
  solution.
* Demote requires dependencies to requires.private when a parent
  dependency is pulled in via requires.private.
* Trim trailing whitespace when processing package arguments.
* Avoid strncmp() in --modversion version comparison.
* Update autoconf compile flag checking macro.
* Add system default path configuration to Meson.
* Fix order of PKG_CONFIG_LIBDIR and PKG_CONFIG_PATH element processing.

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>