Setting HAPROXY_CFLAGS on the haproxy build command line overrides CFLAGS
which were internally set by the haproxy Makefile.
Among those omitted CFLAGS is -fwrapv. Compiling haproxy without it and
and then running the program results in runtime error:
$ haproxy
FATAL ERROR: invalid code detected -- cannot go further, please recompile!
...
To address this issue, include HAPROXY_CFLAGS in the DEFINE variable instead
of CFLAGS in haproxy.mk.
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>