Don't set CPPFLAGS or anything like it in Makefile.am. These are set in
confingure.ac. Also, there's rules about which ones the user sets and which one
the build system sets. E.g. I think CFLAGS is reserved for the build system,
but CPPFLAGS reserved for the user.
HTH,
Gabriel
Not so much user-reserved vs. build system-reserved:
CPPFLAGS are for the C preprocessor, so -Ddefines and -I includepaths would be preprocessor flags. CFLAGS would be for C compiler flags, e.g. optimization or architecure flags.