Pkgconf

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

* Fix additional logic errors relating to the new fragment trees
functionality.

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

* Fix several logic errors in the pkg-config file parser that were
surfaced by recent refactoring work.

* Fix BSD make compatibility so that it generates the test data
before running kyua on BSD make implementations.

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

* Ensure the full DAG is solved for all query types.

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

* Allow multiple package names in solution-based queries such as
`--print-requires`, `--print-requires-private` and `--print-provides`.

* Use `_DEFAULT_SOURCE` where appropriate on Meson.

* Add an abstract buffer type and use it when loading files from disk
instead of a 64KB buffer. This ensures large pkg-config files are
not truncated.

* Disable graph recursion in `--variable` queries as it was generating
duplicate output.

* Add infrastructure for tracking fragment group relations and convert
storage of fragments to use a tree-like structure instead of string
concatenation.

* Add support for tracking linker groups, e.g.

-Wl,--start-group -la -lb -lc -Wl,--end-group

as fragment groups.

* Properly contextualize the sysroot directory when processing package
information, ensuring packages where ${pc_sysrootdir} does not match
the default are properly processed.

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

* 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.