addon_config.make update

[Jonathhhan]

I adopted the flags from current ofxPd (also the style). Maybe check if it does not break anything / evrything is needed.
Feel free to keep the old style.
But what I need to add to make it work (at least for compiling with Emscripten) is:

ADDON_CFLAGS = -DPD_INTERNAL
# this is included directly in pd~.c, don't build twice
ADDON_SOURCES_EXCLUDE += libs/ofxPd/libs/libpd/pure-data/extra/pd~/binarymsg.c
# not needed
ADDON_SOURCES_EXCLUDE += libs/ofxPd/libs/libpd/pure-data/src/m_dispatch_gen.c

[Jonathhhan]

I guess this won't be needed, because m_dispatch_gen.c is excluded in current libpd anyways (which was not the case, when I made this PR).