This fixes path relocation in mingw environment. Without this,
libdir and includedir are not shown in pkgconfig output. e.g.
* Without predefined variables:
- pkgconf -cflags jack: No output
- pkgconf -libs jack: -ljack64
* With predefined variables:
- pkgconf -cflags jack: -IC:/msys64/mingw64/include
- pkgconf -libs jack: -LC:/msys64/mingw64/lib -ljack64
Also official documentation suggests to use variables
https://people.freedesktop.org/~dbn/pkg-config-guide.html
jack.pc.in:
Add the custom `jack_implementation=jack2` pkgconfig variable to the
generated jack.pc file to be able to distinguish jack implementations.
As jack implementations exist with jack1, jack2 and pipewire-jack, it is
not (easily) possible to distinguish them by looking at the version
alone (particularly the case with jack2 vs. pipewire-jack, as they share
the same headers).
Nedko Arnaudov
Biswapriyo Nath
David Runge
falkTX
nedko