Bug#658929: Please enable hardened build flags

[Fabian Greffrath]

Thanks Fabrice!

> CFLAGS=-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat
> -Wformat-security -Werror=format-security
> CPPFLAGS=-D_FORTIFY_SOURCE=2
> CXXFLAGS=-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat
> -Wformat-security -Werror=format-security
> FFLAGS=-g -O2
> LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro

So it looks like -Wl,-Bsymbolic-functions is the only flag added to
LDFLAGS. And if I filter this out in debian/confflags, things *should*
work...