Pkgconf

----------------------------

* Documentation fixes from Sam James and Stefan Weil.

* Fix --modversion with constraints.
Patch by Kai Pastor.

* Reintroduce an optimization to the dependency graph walker which avoids
revisiting already visited nodes.
Patch by Yi Chou with some modifications.

* Add a regression test to check that the dependency flattener is working
as expected.
Patch by Kai Pastor.

----------------------------

* Do not flatten the solver solution into the original world used as
input to the solver.
Patches by Kai Pastor.

* Fix warnings with GCC 14 -Walloc-size.
Patch by Sam James.

* 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.
Patch by Colin Gillespie.

* Avoid strncmp() in --modversion version comparison.
Patch by Colin Gillespie.

* Update autoconf compile flag checking macro.
Patch by Peter Kokot.

* Add system default path configuration to Meson.
Patch by L. E. Segovia.

* Fix order of PKG_CONFIG_LIBDIR and PKG_CONFIG_PATH element processing.

----------------------------

* Fix some edge-cases with the new `--modversion` implementation
and add additional regression tests.
Patch by Colin Gillespie.

* Fix some format specifiers to use PRIu64 in debug tracing.

----------------------------

* Fix long-standing bug where package identifiers for "uninstalled"
packages incorrectly included the "-uninstalled" suffix.

This was exposed by the recent change to `--modversion` in 2.0.1.

----------------------------

* The behavior of --modversion was largely reverted back to the traditional
pkg-config behavior, but still operates on a solved dependency graph.

The order of --modversion output is based on the dependency resolution
queue which is passed to the solver, which itself generally maps to the
order of the constrants provided on the command line.

* A new flag, --verbose, has been added. When used with `--modversion`, it
is possible to disambiguate which version belongs to which module:

% pkgconf --modversion --verbose foo bar
foo: 1.2.3
bar: 1.3

----------------------------

* When flattening the dependency graph, retain the latest seen edges
rather than the earliest.

* Fix a long-standing bug where the dependency resolution queue was
evaluated in reverse. This bug masked the aforementioned dependency
flattening bug in many cases.

* Fix handling of --with-path, which was appending paths to the search
list rather than prepending them as intended.

* Error when --modversion is requested with more than one package, as
the output is ambiguous.