Pkgconf

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

* Fix compile with Meson on Solaris by defining __EXTENSIONS__.

* Add support for the PKG_CONFIG_RELOCATE_PATHS environmental variable.
When set, the program will act as if --define-prefix is always enabled.

* Color solution nodes that were part of the original query, and use
that coloring to skip over dependencies when generating DocumentNames
in bomtool.

* Enhance --env option to support variables with both --variable=varname
and --print-variables.

* Add --exists-cflags option which creates synthetic preprocessor
definition flags for every queried dependency when found.

* Document that Requires.private is always used for header paths.
Patch by Petr Písař.

* Fix minor documentation typos.
Patch by Pierce.

* Ensure string comparisons using <ctype.h> functions are done with
unsigned bytes to avoid undefined behavior.
Patch by Taylor R Campbell.

* Fix parsing edge-case bugs with dependency versions.
Patch by Kai Pastor.

* Change PKG_PROG_PKG_CONFIG autoconf macro to add a customizable
failure handler if pkg-config is not found.
Patch by Ismael Luceno.

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

* libpkgconf SOVERSION is now 5.

* Significant solver rework to flatten both requires and requires.private
dependencies in a single pass. Improves performance slightly and ensures
proper dependency order.
Patches by Kai Pastor.

* Improve `--digraph` output to reflect more of the solver's state in the
rendered dependency graph.
Patches by Kai Pastor.

* Do not reference the graph root by name when presenting error messages about
directly requested dependency nodes.
Patch by Kai Pastor.

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

* 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.