Hello,
>pkg-config --cflags also just outputs -I/usr/include/<package>.
>Does pkgconfig support multiple paths like this?
add the triplet to your .pc shipped file
/usr/lib/x86_64-linux-gnu/pkgconfig/python-3.6m.pc:Cflags:
-I${includedir}/python3.6m -I${includedir}/x86_64-linux-gnu/python3.6m
Other programs do this too, so with some sort of patch this should be possible
(they are sometimes created during build, otherwise you will need some sed
during install or similar
G.

