byterun/Makefile: add preprocessor flags to the right varialbes
byterun/Makefile: add preprocessor flags to the right varialbes

A few -D and -I flags were added to OC_CFLAGS while they should be added
to OC_CPPFLAGS

As a consequence, there is no need to pass OC_CFLAGS to the compiler
when computing dependencies for C files.

gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml