The configure script generates config.mak, which has the variable
CFLAGS set to -O2 by default, or any other value if the user chooses to
enter --extra-cflags. But Makefile will discard it, unless you have +=
instead of =. Also removed -O2 from Makefile, as it is default on
config.mak. The user might want to try something else.
I am sending the patch in the mail and attached, I don't know how you preffer it.