Add include path for LV2

[runiq]

I'm trying to package Ratatouille for Flatpak and this was the first hurdle.

[brummer10]

Usually pgk-config lv2 comes out empty and the lv2 header been found in the system include path. If it does something for a flatpack build, I think it is better to keep it as a patch there.

[runiq]

That's fair, I can do that. But... why do that only for the LV2 headers? Libsndfile, Cairo, etc. appear to bell handled by pkg-config as well.

[brummer10]

lv2 isn't a library, it's "just" a set of header files, so it doesn't comes with a lv2.pc file. cairo and sndfile does that and implement this way there own dependencies. For example cairo gives:

pkg-config --cflags --libs cairo
-I/usr/include/cairo -I/usr/include/libpng16 -I/usr/include/freetype2 -I/usr/include/pixman-1 -lcairo

while pkg-config --cflags --libs lv2 return empty with regular lv2 instalation. So, when adding lv2 to the pkg-config flags helps on flatpack, flatpack would properly added a pc file for lv2. The usual way to use the lv2 headers is to just include them via the include path of the host system, no linking is needed, hence no ldfalgs to add.

[runiq]

I'll have to noodle on this a bit, but it makes sense. Thanks for the explanation, and for your patience. :)