Hello Sedric!
    Thank you for the tips. I got plotmm to compile. But I'm finally
    and utterly
 giving up on EQ10Q. I don't know, what is wrong with this software.
 But loads
 of paths seem wrong for it. It didn't find my lv2-c++-tools and other
 libraries, all installed from system packages. I had to link
 directories like:
 /usr/include/glibmm-2.4/glibmm -> /usr/include/glibmm
    But there were always nmore and then some single include files.
    I'm sick of
 it. I think I can continue to live well with Fons' parametric 4-band
 EQ.
    Again thanks for the hints and everything!
    Warmly yours
          Julien 
as you wish.
But did you install the various "dev" packages?
You should have "*.pc" files in a directory called
"pkgconfig/" below "*/lib/", wherever that's installed
in debian (/usr/lib/pkgconfig seems reasonable).
My compiling created lv2-gui.pc, lv2-plugin.pc,
paq.pc (for lv2-c++-tools as it seems), and
plotmm.pc.
Maybe you can search for those in your system paths...
Anyway, happy music!