pkg-config is a script to make putting together all the build
flags when compiling/linking a lot easier.

Report bugs at https://gitlab.freedesktop.org/pkg-config/pkg-config/-/issues

To use pkg-config, do something like the following in your configure.ac

    PKG_CHECK_MODULES([GNOME], [gtk > 1.2.8 gnomeui >= 1.2.0])

This puts the neccesary include flags to compile/link something against
libgnomeui and all its dependencies in $(GNOME_CFLAGS), and the -L/-l flags
for linking in $(GNOME_LIBS).

Users can define the PKG_CONFIG environment variable to point at the
right one, or if they cross-compile and have a correctly named pkg-config
(eg. arm-linux-pkg-config) in their PATH that will be used in preference.

Users can also define the GNOME_CFLAGS and GNOME_LIBS environment variables
if they think they know better, pkg-config will not be called if they do
that.

The "gtk > 1.2.8" part is only neccesary if you want to specifically check
if libgtk is version 1.2.8 or higher. Otherwise, the flags for gtk
will be included automatically, since libgnomeui depends on gtk.
So you could just say:

     PKG_CHECK_MODULES([GNOME], [gnomeui])

for any version of gnomeui.

For more info, there's even a man page, try 'man pkg-config'

Building
========
pkg-config depends on glib.  Note that glib build-depends on pkg-config,
but you can just set the corresponding environment variables (ZLIB_LIBS,
ZLIB_CFLAGS are the only needed ones when this is written) to build it.

pkg-config also either needs an earlier version of itself to find glib
or you need to set GLIB_CFLAGS and GLIB_LIBS to the correct values for
where it's installed in your system.

If this requirement is too cumbersome, a bundled copy of a recent glib
stable release is included. Pass --with-internal-glib to configure to
use this copy.

If you're cross-compiling and you need to build the bundled glib, refer
to the glib documentation for cross-compiling glib. In short, this will
require setting some autoconf cache variables in cases where glib would
need to run a program to determine the correct value. See the glib
documentation:

https://developer.gnome.org/glib/stable/glib-cross-compiling.html

If you need to use the bundled glib on Mac OS X, you'll most likely need
to build for a single architecture rather than as a universal binary.
This is because glib (as of version 2.32) does not support building for
multiple architectures out of the box. The glib2 from MacPorts or
Homebrew may be available as a universal binary and usable for
pkg-config as described above. Nothing in pkg-config itself precludes
being built as a universal binary.